Information: Instructions for Use of DM8 Vibration Density Meter

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1. Overview In industrial production, liquid density is an important physical property that needs to be measured; in particular, its measurement is essential in electronics factories, chemical plants, oil refineries, and food processing plants. The new DM8 vibrating densitometer features high reliability and a wide range of operational functions. The instrument consists of detectors and a converter. The detectors include vibrators and RTDs (resistive temperature detectors), which output density signals (frequency) and temperature signals (voltage) to the converter. The converter uses a microprocessor to convert the frequency signals of the density values sent from the detectors and to display them; it can also calculate the density of these signals at a reference temperature and display it numerically. In addition to outputting analog signals, the converter can also output digital transmission signals and provide various functions. Such as – contact verification, self-diagnosis, etc. 1.1 Technical Standard Specifications 1.1.1 Object of measurement: Liquid density. Principle of measurement: Vibrational density measurement. Measurement range: Density: 0.5~2.0 g/cm3; Temperature: -10~100°C. Distance between detector and converter: Less than 2 km. Power supply: 90~132VAC or 180~264VAC, 50/60HZ. Power consumption: 20VA. Characteristics: Repeatability: 5×10-4 g/cm3 (for digital output); 1% of the range (for analog output). Linearity: ±0.5% of the range (when the range is 0.2 g/cm3 or less); ±1% of the range (when the range is 0.2~0.5 g/cm3). Temperature characteristics: ±0.5%/±10°C change. Flow rate characteristics: ±0.1% within the range of 0–5 g/min. Pressure characteristics: variation of ±0.0005 g/cm3 to ±1 kg/cm3. Viscosity error: ±0.1% within the range of 0–1500 CP.
1.1.2 Detector
Standard density meter: Model VD6D. Detector construction: not explosion-proof or weather-resistant. Shell material: aluminum alloy casting. Shell color: emerald green (equivalent to 7.5BG4/1.5 on the Munsell color scale). Shell lining: baked-on epoxy resin. Weight: approximately 12 kg. Installation: mounted on 2-inch pipes (JIS50A standard). Operating temperature range: -10–50°C. Vibrator material: stainless steel JIS SOS316 or nickel. Temperature of the liquid being measured: -10–100°C. Pressure of the liquid being measured: up to 2 Mpa (equivalent to 20 kg/C㎡G). Maximum pressure: 5 Mpa (equivalent to 50 kg/C㎡G). Steam heating available. Process connection: JIS PT 1/4 male thread. Electrical connection: JIS PF 3/4 male thread.
Explosion-proof detector: Model VD6DF. Detector construction: JISd2G3 explosion-proof design or FM-approved explosion-proof design. Electrical connection: JIS PF 3/4 male thread or 3/4 NSM male thread. Note: All other specifications are the same as those for the standard model mentioned in point (1), except for the explosion-proof design.
Hygienic model detector: Model VD6S. Process connection: special connection using JIS6A pipes with a nominal diameter of 6 mm. Steam heating not available. Note: All other specifications are the same as those for the standard model mentioned in point (1), except for these two points.
1.1.3 Converter: Model DM8C. Shell construction: dust- and weather-resistant. Color of the front panel: equivalent to 2.8GY6.4/0.9 on the Munsell color scale. Color of the shell: equivalent to 2.8GY3.1/0.5 on the Munsell color scale. Shell lining: baked-on epoxy resin. Installation: can be installed on panels, walls, or JIS50A pipes. Weight: approximately 7.5 kg. Operating temperature range: -10–50°C. Display: digital display, 5-digit LED display. Displayed value: density value after conversion at the reference temperature ； Measure the density at the given temperature (g/cm3); measure the liquid temperature (°C) to verify the set value for liquid density (displayed upon request) ； Calibrated liquid temperature coefficient setting value *10-5 g/cm3/℃ (call to display); lower limit of output range (%) (call to display) ； Upper limit of output range (g/cm3) (call to display); reference temperature (℃) (call to display) ； Measure the set value of the liquid temperature coefficient (-1*10-5 g/cm3/℃) (call to display); detector coefficients A and B (call to display) ； Detector calibration coefficients C, D (call to display) ； Fault details display ； Analog output signals: 4–20 mA for temperature in °C and 0–1 V for temperature in °C; density converted at the reference temperature; range: 0.05–g/cm³. Interface for digital output signals: RS-232C. (1) Communication standard: Asynchronous system. Start bit: 1; Stop bit: 2; Parity: None. Data transmission rate: 1200 bits/s. Transmission format: ASCII; character length: 8 bits. Wiring system: Two-wire output. (2) Output signals: Content transmitted includes measurement data (density converted at the reference temperature in g/cm³; density at the measured temperature in g/cm³; temperature of the liquid being measured in °C; calibration status [calibration started, error code, calibration completed]; fault alarms [error code]). Signal levels: Output voltage: ON, 9±3 V; OFF, -9±3 V. Output impedance: 300 ohms. Output format: Measurement data: #*.**** **** ***.*CRLF. (Note: Data is output in the order of density converted at the reference temperature, density at the measured temperature, and temperature of the liquid. In calibration or maintenance mode, saved data (valid values during input/output mode) is output; once switching to calibration or maintenance mode, the saved data is immediately erased.) Calibration status: #CALIBRATION START CRLF. (Note: No data is output during calibration; however, when a parameter error occurs, the output becomes as follows: #ERROR *CRLF (*:5.0r6) #CALIBRATION END CRLF.) Fault alarms: #ERROR *ERROR *......CRLF. (Note: When multiple errors occur, the corresponding error codes are output. Example: #ERROR-1 ERROR 3CRLF.) Contact output in abnormal states: Single normally open contact (16); maximum voltage: 220 V DC, 250 V AC; maximum current: 2 A (for resistive loads); maximum contact voltage: 60 W. Abnormalities detected: Abnormalities in the detector and converter. Saving of output signals: Data is saved during calibration (CAL) and maintenance (MAIT) modes; in case of a fault, 10% less data is saved. Temperature coefficient range: 0–0.002 g/cm³/°C. Calibration method: One-touch calibration by setting the liquid density. Air purge connection: JIS PT1/8, PT1/4 male threads or 1/4 NPT male threads (optional). Cable inlet II: Diameter 27 mm, five holes, covered with four waterproof plugs equivalent to JISA15 and one plastic waterproof plug equivalent to JISA20 (accessories). Power supply: 90–132 VAC or 180–264 VAC, 50/60 Hz. 1.1.4 Special cable: DM8W type; model: six-core double-shielded cable. Insulation: Polyethylene; sheath: Polyvinyl chloride. Insulation resistance: 1000 Me/km. Conductor resistance: 15.3 ohms/km. Outer diameter: 15.8 mm. 1.1.5 Accessories: Syringe for injecting the liquid to be measured – 1 piece; Brush (for cleaning the vibrator) – 1 piece; Hex screwdriver for opening the wiring box – 1 piece; Hex wrench for removing the detector cover – 1 piece; Desiccant – 2 pieces; Fuse for the converter – 1 piece. 1.2 Model numbers and suffix symbols: 1.22 Fire-resistant detector; 1.2.3 Hygienic detector; 1.2.4 Converter; 1.2.5 Special cable. 1.3 External dimensions: 1.3.1 Detector; 1.2.3 Hygienic detector; 1.2.4 Converter; 1.2.5 Special cable. 1.3 External dimensions: 1.3.1 Detector. Ordinary fire-resistant type. Figure 1.4 Precautions for using fire-resistant and explosion-proof instruments. 1.4.1 Overview of fire-resistant instruments. The technical standards for explosion-proof instruments comply with the regulations of relevant international organizations. The DM8 vibrating liquid density meter includes a detector and a converter. The VD6DF density detector explosion-proof instrument can be installed in areas with explosive gases. It must be noted that the installation method, environmental conditions, and use of the instruments must comply with the regulations of relevant international organizations. When using the VD6DF detector in hazardous areas, strict attention must be paid to the explosion-proof regulations and the warning signs on the analytical instrument. (Note): The VD6D and VD6S type density detectors cannot be installed in hazardous areas if they are not explosion-proof instruments. The VD6DF density detector complies with either JIS or FM explosion-proof and fire-resistant technical standards. JIS is the testing of civil fire-resistant electronic equipment specified by the Labor Safety and Health Regulations (Japan), conducted under the oversight of the Public Administration Agency. The FM-type explosion-proof design has been certified to meet the National Electrical Code (NEC) of the Factory Mutual Research Institute (FM), and it also complies with the requirements of OSHA (the U.S. Occupational Safety and Health Administration). 1.4.2–1.4.6 contain general precautions for using the VD6DF density detector; for more detailed information, please refer to the following entries. JIS fireproof requirements recommend the use of electrical equipment in areas with explosive gases, as specified by the Industrial Safety Research Association and the Ministry of Labor. FM fire-resistant requirements: Chapter 5 of the American Electrical Code, Special Occupancies. 1.4.2 Marking for explosion protection instructions: The data plate of the explosion-proof design of the VD6DF density detector includes the approval number, model code, and range of ambient operating temperatures. Technical specifications for FM explosion-proof standards: The data plate of the VD6DF density detector complies with explosion-proof technical standards; it bears approval markings, the hazard zone classification, the operating temperature range, and precautions for use. 1.4.3 Installation area and environmental conditions The VD6DF density detector can be installed in hazardous areas with specified gases. However, it cannot be installed in areas where explosive gases are present continuously, or where gases accumulate over a prolonged period in amounts equal to or exceeding the minimum explosive limit of those gases. The environmental conditions at the location where the detector is installed are very important; before installing the detector, it is necessary to check the temperature, humidity, and altitude in the area surrounding it. None of these conditions may exceed the specified limits; the temperature range indicated on the data panel is (-10–50°C), the altitude should be below 1000 meters, and the relative humidity should be between 45% and 85%. 1.4.4 External wiring work: The external wiring of fire-resistant detectors must be carried out using fire-resistant metal conduit wiring methods, whereas JIS explosion-proof technology and fire-sealed types use external cables. 1.4.5 Maintenance steps: Do not open the cover of the detector if the power supply has not been turned off. If it is not possible to turn off the power supply, check immediately whether there are any hazardous gases in the area surrounding the detector. 1.4.6 Repair During repair, the following points must be taken into account: The detector must be restored to its original condition, maintaining fire-resistant properties both electrically and mechanically. The performance of fire-resistant instruments is determined by important factors such as the gap, the length of the tubing, and the mechanical strength of the enclosure. Therefore, the repair personnel must be careful not to damage the surface or impact the casing. 2 Working Principle 2.1.1 Density Detector The VD6DF type detector is a vibrating densitometer; its principle of operation is that the density of the liquid inside the tube is related to the frequency of the tube’s lateral free vibrations. Assuming a tube filled with liquid, as shown in Figure 2.1, the formula for the natural transverse oscillation frequency of such a tube is as follows: Figure 2.1 Equation (1) Fx: Natural propagation oscillation frequency (Hz) C: Constant related to the mode of oscillation L: Length of the oscillating tube (m) E: Young’s modulus of the tube material (kg/m2) P1: Density of the tube material (kg/m3) ρx: Density of the liquid inside the tube (kg/m3) D1: Outer diameter of the tube (m) D2: Inner diameter of the tube (m) In Equation (1), aside from Fx and ρx, all other parameters are determined by the material and structure of the tube. Thus, the density Px of the liquid is obtained by measuring the free conduction oscillation frequency Fx of the measuring tube. 2.1 Transducer: The density transducer calculates the liquid density using an oscillation frequency signal and a voltage corresponding to temperature. In Equation (1), L.E.P1D1D2 or ρx is a function of the liquid temperature; therefore, Fx is also a function of temperature. The functions A(t) and B(t) serve for temperature compensation, enabling the correct density to be obtained. Their formulas are given in Equation (2). Here: A(t) = A1(1.0060 – 1.98*10^-4T – 9.7683*10^-8); B(t) = B1. A1 = (A + 131072)/100, and B1 = B/30000. T represents the liquid temperature. Note that the constants A and B of the detector are fixed values. (2) He (3) It can be seen that ρx = … In equation (3), ρx represents the density of the liquid at the measurement temperature; the density ρTB at the reference temperature can be obtained using equation (4). ρTB = ρx + α(TX – TB) (4) Where α is the temperature coefficient of the liquid’s density, TB is the reference temperature (°C), and TX is the temperature of the liquid at the time of density measurement (°C). 2.2 Main components 2.2.1 Density detector Figure 2.2 shows a schematic diagram of the density detector. As illustrated, the density detector consists mainly of a vibrator, capacitive sensing electrodes, and an amplifier. The vibrator consists of two sampling tubes whose upper ends are connected to the base. The connector is equipped with an RTD to measure the temperature of the sampling liquid, and the vibrator also includes a piezoelectric element to oscillate at a frequency corresponding to the density of the sampling liquid. Figure 2.2 The capacitive sensing electrode is installed between two vibrating tubes to detect the transverse oscillation frequency of the vibrating tubes. The amplifier converts the output signal from the capacitive sensing electrode into an alternating voltage and amplifies it. The RTD temperature signal of this frequency signal is transmitted to the converter, while a portion of the frequency signal is fed back to the piezoelectric element to maintain the oscillation of the vibrator. 2.2.2 Density Converter Figure 2.3 shows the block diagram of the density converter. As illustrated, the density converter receives the density signal (frequency) FP and the temperature signal (voltage) VT from the density detector, and outputs an analog 4–20 mA DC signal representing the density of the liquid at a reference temperature, as well as a 0–1 V DC signal. The density at the measurement temperature and at the reference temperature, as well as the digital signal of the measurement temperature, are also outputted. The converter circuit consists of three printed circuit boards. The displayed content and setting constants can be changed using the buttons and toggle switches on the front panel. 3 Installation, piping, and wiring: The DM8 true vibration type density meter includes a density detector and a density converter. The density detector is generally installed in the area near the sampling tube that guides the measuring liquid, while the density converter is usually placed near the density detector; it is not installed in a hazardous area but can be located in the control room, even though it is far away from the detector that receives digital signals. 3.1 Installation of the density detector: As specified, the density detector should be delivered together with the sampling unit. If the detector does not come with a sampling unit, the user must install a sampling device on their own to match it with the measurement system. 3.1.1 Fixing the density detector: When the detector lacks a sampling unit, it must be installed vertically {Note 1}. The pipe fixing brackets make it easy to install it on either horizontal or vertical pipes {JIS50A}, as shown in Figures 3.1 and 3.2. {Note 1}: The detector must be installed vertically to keep the vibration tube in a vertical position. (1) Installed on a pipe: The pipe mounting bracket is attached to the detector and installed on a vertical pipe. If it is to be installed on a horizontal pipe, the mounting bracket is removed from the detector, rotated 90 degrees, and reattached to the detector, as shown in Figure 3. 1 is installed on a vertical pipe, while Figure 3.2 shows it installed on a horizontal pipe. (2) Installed on a bracket – this bracket is not a pipe mounting bracket; loosen the four bolts (with spring washers) ； Remove the tube mounting bracket from the detector. Then, use four bolts (with spring washers) to fix the detector to the bracket according to Figures 3 and 4; Figures 3 and 3 show the positions of the holes in the bracket. 3.1.2 Sampling unit of the vibrating densitometer This section describes the sampling of the densitometer. The sampling device is equipped with valves, thermometers, flow meters, and so on. And it is installed near the pipes and density detectors. The sampling device is used to measure the density of liquids, providing favorable conditions for monitoring measurements as well as for maintenance tasks such as calibrating and cleaning the vibrator. Install the sampling device as described below; for the piping of the device, refer to Section 3.3. (1) Flowchart: Figure 3.2 shows the flowchart of a typical sampling device, and the Yokogawa VD6SM sampling unit is also designed based on this flowchart. In Figure 3.5, various components of the sampling device, such as F (filter screen), typically have 80 mesh holes to prevent solids from entering the sampling tube. T (thermometer), FM (flow meter) and P (pressure gauge) are essential for monitoring and measuring liquids. The needle valve “NV1” is used to control the flow rate of the sampling liquid, while the ball valve “BV1” and the needle valve “NV4” are used to shut off the sampling liquid. How to clean the vibrator or calibrate it using a standard solution (the needle valve is used to regulate flow); the “NV2” and “NV3” needle valves are used to drain the liquid from the vibrator or to collect samples for manual analysis. When the viscosity of the liquid being measured is too low and its freezing point is too high, the density detector and the liquid pipeline are preheated gradually. The steam pipe is connected to the density detector, and the liquid pipe is also heated using the steam pipe. ““V1” (the “STOP” valve) supplies steam to the density detector, while “V2” (the “STOP” valve) supplies steam to the heat-mixing tube. ST1 (steam collector) is used to drain condensate water. (Note 1): The various valves used in sampling devices change as their performance changes over time. This manual provides detailed device names (such as ball valves). Used to limit performance. When the device model is not specified (such as a “STOP” valve), the general name is indicated within “”. (Note 2): The standard version of the VD6D density detector and the VD6D (explosion-proof version) are connected by steam pipes, whereas the VD6DS (hygienic version) has no steam connection. (Note 3): The VD6SM sampling unit is manufactured by Yokogawa and is used for the VD6D (standard type) or VD6F (fireproof type) models; the VD6DS (hygienic type) is not recommended for use in food production. Figure 3.5 (2) Key points in the design of the densitometer sampling unit. l Reduce the length of the filling tube to increase responsiveness. l Ensure that no air remains inside the pipeline to avoid errors. Do not bend the tube too much so that solids accumulate. It ensures easy cleaning. The material of the device should be chosen to better suit the liquid being measured, especially in food measurement, where the selection must be precise. Figure 3.6 (3) Installation of the densitometer sampling unit: Attention must be paid to the installation location of the density detector with a sampling unit or the user’s own sampling unit ； l Sampling port near the main pipe; l Vibration avoidance; l Compliance with the environmental conditions of the specified hazardous area (when the detector is of the VD6F fire-resistant type), and the sampling unit is fixed on a concrete base to facilitate drainage. (4) Remove the packaging boards used to transport the density detector; during transportation, secure the vibrator to the amplifier housing to prevent damage. Remove the fixing rubber plate, which is inserted between the housing and the vibrator; follow the steps below to remove this plate. Refer to Section 4.1.1 for the names of the components. (a) Use a hexagonal wrench to remove the fixing screw, loosen the housing counterclockwise and pull out the rubber plate without touching the internal components. (b) Remove the vibrator’s housing (including the desiccant). (c) Use a flat screwdriver to loosen the fixing screw of the vibrator counterclockwise, and ensure it is fully loosened; otherwise, the vibrator may collide with the screw during measurement, resulting in errors. Therefore, since the vibrator is made of thin-walled tubing, be careful not to bend or damage it. (d) Reinstall the casing removed in step (b), and also reattach the casing taken off in step (a); keep the removed rubber sheet for use when measuring transport density. 3.2 Installation of the densitometer converter. 3.2.1 Installation Area The density transducer must be installed in the area described below. (1) The sampling unit is installed in a location that facilitates maintenance and calibration, while the density converter, designed with a dust- and rain-proof structure, can be installed outdoors. If a VD6F fire-resistant detector is used, it cannot be installed in hazardous areas; it must be installed in non-hazardous (safe) areas. Moreover, when using a receiver to accept the digital output signal from the converter, the allowable length of the connection cable between the converter and the receiver is no more than 10m ； (2) Avoid vibration ； The electronic circuit of such a vibrator will malfunction ； (3) Avoid direct sunlight. The operating temperature range for this instrument is -10–55 °C, but the temperature may exceed this range due to direct sunlight in summer ； (4) Avoid installing in areas with corrosive gases and dust. The converter features a dust-proof and waterproof design; it is recommended to install it in an appropriate environment to facilitate maintenance (by opening the front door of the converter). For the same reason, the installation locations for items (5) and (6) below also need to be taken into consideration ； (5) Avoid large temperature fluctuations. (6) Avoid excessive moisture. 3.2.2 Installation of the density converter: The density converter can be installed on a disk surface, a wall surface, or a pipe (JIS50A); the pipe must be fixed vertically to the mounting bracket. See Figure 3.8. Note: The installation posture should not affect the performance of the converter. The installation steps are as follows: Figure (1) – Installation on the disk surface. Before installing it on the disk surface, the mounting brackets of the converter must be removed. The size of the opening in the disk surface is shown in Figure 3.9. Before inserting the converter into the disk surface, remove the brackets on either side of the converter’s housing, then insert the converter into the disk surface and reinstall the brackets in their original positions to secure it in place. See Figure 3.10 (2): Installation on the wall. Before mounting it on the wall, remove the tube mounting bracket of the converter and drill two 8mm screw holes in the wall as shown in Figure 3.11. Use two mounting brackets to attach the converter to the wall, as shown in Figure 3.12(3). Installation on pipes: The mounting brackets are suitable for use on pipes with a nominal diameter of 50A (diameter 60.5 mm); install the converter on vertical pipes according to Figure 3.13. 3.3 Piping: The vibrating densitometer requires the following piping: (1) Sample liquid conduit, (2) Maintenance air pipe, (3) Steam pipe, (4) Air purge pipe. The sample conduit is used to convey the liquid to be measured to the density detector, while the maintenance air pipe is used to blow the liquid out of the vibrator using air during instrument maintenance (such as cleaning the vibrator or performing standard calibrations). The steam pipe is installed as needed to heat the sampling liquid channel ； When the converter is installed in a dusty environment, an air purge pipe needs to be installed. The conduit for the sampling liquid between the main pipe and the sampling tube assembly falls under the piping described here. 3.3.1 Sampling liquid conduit The sampling liquid conduit carries the liquid to be measured to the sampling unit; the main pipe should have two sampling ports (sampling inlet and return port), as shown in Figure 3.14. The sampling inlet tube is connected to the “SAMPLE IN” of the sampling unit, while the return tube is connected to the “SAMPLE OUT” of the sampling unit. The piping steps are as follows: (1) Select the locations for the sampling inlet and the sampling return outlet such that the pressure difference between them is at least 0.1 Mpa, or 1 kg/cm2; (2) The length of the pipe between the sampling inlet and the “SAMPLE IN” port should not exceed 10 meters ； Stainless steel pipes with a nominal diameter of 15 mm or SCH40-80 are to be used. (3) The stop valve and discharge valve are installed near the sampling unit ； (4) Avoid excessive bending of the pipes to prevent residue accumulation ； Figure 3.14 3.3.2 Maintenance air pipe: When cleaning the vibrator or calibrating the densitometer with a standard liquid, air pressure is used to blow out the liquid; clean and dry air at a pressure of (3–5 kg/cm2) must be employed. Install stop valves and pressure relief valves on the air pipe; on the () pipe, connect a copper tube with an outer diameter of 10 mm to the detector, and connect air to the sampling unit to clean the vibrator or calibrate the densitometer using a standard liquid. Figures 3.15, 3.16, 3.3.3 Steam piping: When the freezing point is too high, it is necessary to install steam pipes to heat the liquid being measured, thereby reducing its viscosity. The use of a sampling unit equipped with a steam pipe serves this purpose; the steam pipe is connected to the “STEAMIN” inlet of the sampling unit, and the sampling liquid conduit should also have a steam heating pipe. The steam pressure should be 0.3–0.5 Mpa (3–5 kg/cm2), and the temperature should be 140–160°C. After performing pressure and airtightness tests on the conduit, the heater for the liquid sampling conduit can be installed. The following points should be noted regarding steam-jacketed tubes: (1) After the installation of the jacketed tube for the liquid sampling conduit, all conduits should be able to be heated; the tubes must be wrapped with insulating material, as shown in Figure 3.17. (2) The outlet of the steam collector should be connected to the atmosphere (see Figure 3.18). 3.3.4 Air purge tube: If the density transmitter is installed in a dusty environment, it is recommended to use a purge tube, and it must be continuously purged with clean, dry air at a pressure of 0.05 MPa (0.5 kg/cm2G). Use Ø6*4mm copper and stainless steel tubes to connect to the gas source in order to purge the converter. The connection for the air inlet is PT1/8 male thread; upon special request, PT1/4 male thread or 1/4 NPT male thread can be provided. Figure 3.17 Steam-jacketed heat exchanger; Figure 3.18 Steam collector discharge piping. 3.4 Wiring: The wiring of the vibrating density meter is as follows: (1) Wiring of the detector and converter (using specialized cables); (2) Wiring of the analog output signal; (3) Wiring of the digital output signal (it is recommended that the length be less than 10 m); (4) Wiring of the contact output for fault conditions; (5) Power supply wiring; (6) Grounding wire. Figure 3.19 Block diagram of the wiring. The cable inlet for the density detector is located at the bottom of the wiring box, while the density converter has five cable inlets with a size of 27 mm each. A cable is passed through each inlet. Figure 3.20 shows an example of an assigned inlet. Figure 3.2.1: Wiring diagram of the bit density detector. 3.4.1: Wiring between the detector and the converter. This wiring is carried out using specialized cables of specified length; the cable connections are shown in Figure 3.2.2. Care should be taken to prevent rust and moisture. Figure 3.2.2 Special cable: Use the included wrench to remove the cover of the junction box, insert the special cable into the cable inlet, and then connect the wires to their respective terminals. A flexible fitting is used at the inlet of the density detector; the cable passes from the detector through a metal tube to the outlet. The wiring of the VD6OF explosion-proof detector must comply with the generally recommended practices. Explosion-proof flexible fittings must be used for the internal threads at the detector cable inlet PT3/4. Note: The radial fitting is not necessarily required either; the radial tube should generally not be removed during inspection and maintenance of the detector. Figure 3.2.3 Wiring to the density detector terminals. Figure 3.2.4 Wrench for opening/closing the wiring box cover. Figure 3.25 Explosion-proof flexible fittings (connected to the converter). The converter is installed in the control room or on-site, and the cable entry points are sealed with purge air. The connector is sealed using washers as shown in Figure 3.26, or the entrance of the metal conduit is filled with a sealing silicone mixture; the cable must be housed within a conduit or protective tube to prevent damage to the cable. Figure 3.26 shows the sealed gland for cable insertion; Figure 3.27 shows the cable entry for metal conduits. Figure 3.26 depicts a sealed connection for cable insertion, while Figure 3.27 shows the cable entry point for metal conduits. The specialized cables are inserted into the converter through the entrance on the left, and the wires are connected to their respective terminals. 3.4.2 Wiring of the simulated output signal The converter provides output signals of 4–20 mAdc (load resistance 550 Ω) and 0–1 DVC (load resistance 250 KΩ). It is important to complete the wiring for both scenarios. The wiring can use a two-shield cable (for one signal) or a four-core cable (for two signals). When connecting the cable to the converter, cut 50 mm off the outer sheath of the conductor and attach a M4 threaded terminal. The shield layer of the shielded cable should be connected to the ground wire of the receiver. The wiring method (for metal conduits and others) is the same as in 3.4.1. 3.4.3 Wiring of digital output signals: In addition to outputting analog signals, the DM8C density converter also outputs digital signals via the RS-232C interface (for details on digital signals, refer to the technical specifications in Chapter 1). When using this type of signal, a three-core shielded cable should be used; the length of the cable between the converter and the receiver should be 10 meters or less. The wiring method is the same as that described in 3.4.2, but the insulation at the ends of the wires must be cut back by 80 mm. The reception method is also the same as that described in 3.4.1. 3.4.4 Output wiring for abnormal condition contacts 　　　 When an error occurs due to an abnormal condition in the density measurement system (as shown in Table 4.2), the output contact signal is generated. For the wiring of this contact output, a two-core cable is used; when connecting the cable to the converter, cut 30 mm off the insulation at the end of the cable and attach a terminal with M4 threads. The wiring method is the same as 3.4.1 and can only sense. 3.4.5 Power supply wiring: This wire supplies power to the converter. Use a two-core shielded cable for wiring; the cable connection and wiring method are the same as those in 3.4.2 “Analog output signal”. 3.4.6 Grounding wire: As specified, the enclosures of the density detector and converter must be grounded. The grounding terminal of the detector is on the mounting bracket base, while the converter is at the bottom of the enclosure. Use a wire with a cross-sectional area of 2 mm2 for grounding, and its resistance to ground should be 100 Ω or less (JIS Class 3). 4. Operation 4.1, Component names and functions. 4.1.1 Density detector. Refer to Figure 4.2 for operation. The operation modes specified for the DM8 vibrating density meter are shown in Table 4.1; the measurement mode (DSPL), calibration mode (CAL), and maintenance mode (MAIT) can be switched using the operation mode selector switch. Table 4.1 Operation Modes and Function Numbers
Operation Mode Switch Function Number Content
Display Measurement Mode (DSPL) Display Number Density (at reference temperature) g/cm3 1 Density (measured value) g/cm3 2 Display temperature of the liquid being measured ℃ 3 Set density of calibration fluid □□□□□ g/cm3
Calibration Mode (CAL) 4 Set temperature of calibration fluid 1 □□□□ ℃ 5 Set temperature coefficient of calibration fluid 1 –□□□*10-5/cm3/℃ 6 Start Calibration Mode 1 (by pressing SET key) CAL—1 (after calibration) – display density 7 Set density of calibration fluid 2 □.□□□□ g/cm3 8 Set temperature of calibration fluid 2 □□□□ ℃ 9 Set temperature coefficient of calibration fluid e –□□□*10-5/cm3/℃
A Start Calibration Mode 2 (by pressing SET key) CAL—2 (after calibration) – display density
Maintenance Mode (MAINT) 1 Cancel protection (for probes) 77 2 Display frequency (density) HZ 3 Display frequency (temperature) HZ 4 Check output signal □□□% 5 Check LED when SET key is pressed (LED flashes 5 times) 6 Set lower limit of output range 0.□□□□ g/cm3 7 Set upper limit of output range □.□□□□ g/cm3 8 Set reference temperature of the liquid being measured □□□□ ℃ 9 Set temperature coefficient of the liquid being measured –□□□*10-5/cm3/℃
A Set detector constant A □□□□□ B Set detector constant B □□□□□ C Display detector calibration coefficient (range) D Display detector calibration coefficient (zero point)
(1) Measurement Mode (DSPL): Normal operation mode. In this mode, the analog output represents the density value at the reference temperature. In addition, the density value at the liquid temperature and the liquid temperature are digital outputs. Density value at reference temperature (no function number displayed). Displaying the density at the measured temperature (NO.1) or measuring the liquid temperature (NO.2) can be achieved by selecting the function number. Use the “FONCTION” key to select the FONCTION number. (2) Calibration method (CAL): In the calibration method, the data required for calibration is set or determined. In this mode, the analog and digital outputs are saved (the current values are stored), but the digital output is stopped when the verification function code is “6” or “A”. When the hold is released after the verification calculation is completed, and the function code changes from “6” or “A” to another code, the measurement data is output again. See the figure. Note 1: The density values resulting from temperature conversion are transmitted in digital form, as are the density values at the measurement temperature and the temperature of the liquid being measured (only the density values after conversion are transmitted as analog signals). Note 2: The density converter displays CAL—1 or CAL—2. Figures 4 and 3 show the output states of digital and analog signals; eight function codes ranging from “3” to “A” are provided for use in the verification method (Table 4.1). Among them, ‘6’ and ‘4’ are designated for the checksum calculation, while the others are the data required for input verification. ‘3’: Verify the density value of the solution (g/cm3), or set the density value for the first verification in a second verification step. According to the regulations, this is the density at the reference density. Note: If the relationship between temperature and density is very clear, it is possible to set the density at various temperatures; it is recommended to use density data at a reference temperature that allows for accurate measurement. ‘4’: Enter the temperature of the calibration solution 1 at the reference temperature set at ’3’. ‘5’: Enter -100,000 times the temperature coefficient of calibration liquid 1 in (g/cm3/°C). Note: The temperature coefficient of -0.00086 g/cm3/℃ becomes 086. ‘6’: Press the “SET” key to perform the verification calculation, which also carries out the first check of the two-point verification. Note: Refer to Section 4.4 for the verification steps. ‘7’: Enter the density value (g/cm3) of the second verification solution (Verification Solution 2) used for two-point verification. As specified, the provided density value is based on the same reference temperature as that in ‘4’. Note: If the relationship between density and temperature is very clear, the density at one temperature can be entered. It is recommended to enter a density value at a reference temperature similar to ‘‘4’’ in order to achieve accurate calibration. ‘8’: Enter the temperature of the calibration solution 2 at the reference temperature set at ‘7’. ‘9’: Enter -100,000 times the temperature coefficient of the calibration solution 2. ‘A’: Press the “SET” key to perform the second verification of the two-point check. (3) Maintenance Mode (MAIT): This mode is used to adjust and check operating conditions. In this operating mode, the analog and digital outputs are saved (their current values are retained), with a total of codes from ‘1’ to ‘D’ available for use in this mode (see Table 4.1). ‘‘1’: Prevent changes to functional data due to carelessness; when ‘0’ is displayed, the functional number has not been entered. The operations for ‘solve’ and ‘7’ are related; for example, setting ‘6’ requires setting ‘7’ as well. ‘8’: Sets the reference temperature of the solution to be measured (in °C). ‘9’: Sets the temperature coefficient of the solution to -100,000 times its value, so that it becomes a positive number. Note: Except for purified water, the density is highest at around 4°C, and the temperature coefficient is generally negative. ‘A’: Sets the detector constant A; since this constant is an inherent characteristic of each detector, it is indicated for every detector. Note: The detector constant A changes depending on various calibration adjustments. ‘B’: Sets the detector constant B; as this constant is also an inherent characteristic of each detector, it is indicated for every detector. ‘C’: Indicates whether single-point calibration or two-point calibration is being used. In both cases, the calibration coefficient (range) is displayed as 1. ‘D’: Indicates whether single-point calibration or two-point calibration is being used. For single-point calibration, 0 is displayed; for two-point calibration, the calibration coefficient (zero point) is displayed as a number other than 0. 4.3 Preparation before measurement 4.3.1 Inspection of piping Check the following points: (1) Whether the pressure difference between the sampling ports is greater than (1 kg/cm²) × 0.1 MPa. (2) Whether the diameter of the sampling tubes is appropriate and whether their length is too great. Note: The sampling inlet tubes are usually made of JJS15A or SCh40–80 stainless steel pipes, and the length from the sampling port to the detector should not exceed 10 m. (3) Whether valves and instruments (such as pressure gauges and thermometers) are installed on the sampling tubes during normal operation and maintenance. (4) Whether air has been used to clean the detector. Note: Cleaning the detector requires dry air with a pressure of (3–5 kg/cmG) × 0.3–0.5 MPa. (5) Whether it is possible to stop the heating steam supplied to the density detector during operation. 4.3.2 Check wiring Check the wiring of the completed measurement system, including the receivers (such as recorders). When the detector is explosion-proof, it must be resealed after the cover is opened. 4.3.3 Measuring liquid flow The procedure for introducing the sample liquid is shown below; the piping required for sampling is illustrated in Sections 3.5 and 3.12. When the arrangement of the tubes is different from that in Figure 3.5, perform the corresponding operations described here. It is very important that there are no bubbles left inside the tube. If calibration is performed using a standard solution, the measuring liquid can be introduced for calibration without cleaning the vibrator; however, if pressure compensation is required (see Section 4.3.6), the measuring liquid is introduced to obtain the compensation value in advance. (1) First, set the states of each valve in the sampling unit as follows: Ball valve “BV1”: Fully closed. Needle valve “NV1”: Fully closed. Needle valve “NV2”: Fully closed. Needle valve “NV3”: Fully closed. Needle valve “NV4”: Fully closed. Globe valve “Valve V1”: Fully closed. Globe valve “Valve V2”: Fully closed. Note: V1 and V2 marked with * are used only when steam heating is applied. (2) The sampling conduit is equipped with a steam heating tube; the valve of the main steam pipe is opened to heat the sampling conduit. Keep the “STOP” valve “V1” closed; do not heat the detector unless it is too cold. (3) Prepare a collection container (liquid dish) in advance and place it under the discharge valve of the sampling tube. First, fully open the discharge valve, then gradually open the ‘tap’ valve; once the sampling liquid begins to flow through the discharge valve, close the ‘tap’ valve. (4) Repeat the steps in (3) for the sampling return tube. Prepare a collection container (liquid dish) in advance and place it under the discharge valve. First, fully open the discharge valve, then gradually open the stop valve; once the sampling liquid begins to flow through the discharge valve, close the stop valve. (5) Fully open the ball valve ‘BV1’ and the needle valve ‘NV4’ of the sampling unit; partially open the needle valve ‘NV1’. Close the discharge valve that was opened in step (3), and gradually open the ‘tap’ valve on the sampling inlet pipe. Once the sampling liquid begins to flow through the discharge valve on the return pipe and no air remains in the liquid, fully open the ‘stop’ valve and completely close the discharge valve. (6) Open the needle valve ‘NV2’ to discharge the residual air from the pipe; once no air-containing sample fluid flows through the outlet, fully close the needle valve ‘NV2’. (7) Adjust the opening of the needle valve “NV1” so that the flow rate through the detector is approximately 5 l/min; the flow rate is indicated by the Yokogawa VD6SM sampling unit and FM flow meter. The flow rate varies with the viscosity of the sampled liquid. If the viscosity of the liquid being sampled is too high, the flow rate indicated will also be higher than the actual flow rate (see Figure 4.4). (8) Ensure that the temperature T and pressure P of the sampled liquid are within the specified ranges. (9) Be careful to ensure that the sampled liquid does not leak from the connection point. Figure 4.4 4.3.4 Power Supply: Supplies the converter as well as the receiver, recorder, computer, etc., with power of the specified voltage and frequency. The receiver must be prepared to receive data, and the controller must be calibrated to enable accurate control. 4.3.5 Data Input: Set the operation mode switch to “MAIT” (maintenance mode) and enter the data (in the states of function codes ‘6’, ‘7’, ‘8’, ‘9’, ‘0’, ‘A’, ‘B’). For details on data input, see Section 4.2. Enter data using the ‘SHDFT’, ‘1NCR’ and ‘SET’ keys; for specific operations of these keys, see Section 4.12. When the temperature coefficient of the liquid to be measured is still unknown while in function ‘9’, please refer to item 4.4.2 Liquid Sampling Calibration (2). 4.3.6 Pressure compensation Pressure compensation is used to account for the changes that occur during measurement under working pressure. Compensation can only be performed when calibration is carried out at atmospheric pressure. The effect of a pressure difference of 0.1 Mpa (1 kg/cm2) on the measurement value is within ±0.00005 g/cm3; therefore, for liquids whose operating pressure is approximately atmospheric pressure, the calibration values at atmospheric pressure can be used. Pressure compensation is used to reduce the effects of high working pressure. Compensatory data is obtained by sampling the liquid. When the density is stable, proceed with the measurement data following the steps outlined in Section 4.3.3 for sampling the liquid. (1) Fully open the needle valve “NV4” and read the pressure of the gauge; simultaneously, the density at the reference temperature is displayed on the converter. (2) Fully open the ball valve “BV1” and open the needle valve “NV3” to equalize the pressure of the liquid sampled by the detector with atmospheric pressure, thereby obtaining a density reading at the reference temperature on the converter. (3) Use the densities obtained from (1) and (2) to calculate the compensation data. Compensation data (kg/cm3) = Density at operating pressure — Density at atmospheric pressure. During verification, the compensation data must be subtracted from the density of the standard solution. 4.3.7 Preparation before receiving digital signals When digital signals are used, a receiver is provided to display or print the transmitted data. The example below is a program that uses the NEC personal computer PC9801 to print Figure 4.5. Figure 4.5 10 ******************************************************* 20 SAMPLE PROGRAM 30 ******************************************************* 40 WIDTH 80,25 50 CLS 60 PRINT *********** RS—232C OUTPUT******************** 70 PRINT: PRINT “(g/cm**3） (℃)”: PRINT 80 OPEN “COM:N82” AS #1 90 LINE INPUT #1 AS 100 PRINT A$ 110 GOTO 90 120 CLOSE #1 130 END Note 1: The value 80 indicates that in “COM:N82”, N means no parity check; 8 refers to 8 data bits, and 2 means 2 stop bits. Note 2: Settings for storage switch: Coefficient: invalid. Communication mode: one-way. Data bits: 8. Parity check: not used. Stop bits: 2. Baud rate: 1200 baud. 4.4 Calibration It is necessary to calibrate the vibrating density meter in order to maintain the specified accuracy. There are two methods of verification: single-point verification and two-point verification. Their respective calibration methods involve using either a sampled liquid or a standard liquid for calibration. Using sampled liquid does not require stopping operation, but pressure compensation is needed for accurate measurement. On the other hand, with standard liquids for calibration, once the density of the solution is determined to be stable, there is no need to repeat the density testing of the sampled liquid in the laboratory. Single-point verification means omitting the second verification in two-point verification. In this way, a two-point calibration using a standard solution and the sampled liquid is performed. The description is as follows: Since what is described here is a density converter installed near the density detector, if the density converter is installed far away from the density detector, please refer to the accompanying instruction manual and carry out the calibration according to its instructions. 4.4.1 Calibration with standard liquids Two standard solutions with known densities at the reference temperature are provided. One density (standard solution 1) must be close to the lower limit of the measurement range, while the other density (standard solution 2) should be close to the upper limit of the measurement range. The temperature and coefficient (g/cm3/°C) of these standard solutions must be known in advance. (*1) When measuring the density of the standard solution, a densitometer with a minimum scale of 0.0005 kg/cm3 is used. The verification must follow the procedures below: during verification, only by stopping the operation of the detector and converter can the instrument that receives the output signal from the converter be shut down. (1) Set the converter to the “CAL” mode and enter the corresponding data for functions numbered 3, 4, 5, 7, 8, and 9. For pressure compensation, subtract the compensation value from the density of the standard solution obtained in 4.3.6. And set to function numbers 3 and 7. (Note): When the compensation value is negative, the set value becomes greater than the density of the standard solution. (2) Blow out the interior of the vibrator with air as follows: fully open the ball valve “BV1” and needle valves “NV4” of the entire sampling unit, fully open needle valves “NV2” and “NV3”, connect an air pipe to the outlet of needle valve “NV3”, and blow out with air at a pressure of 0.2–0.3 MPa (2–3 kg/cm2) for 1–2 minutes. (*2): The sampled liquid remaining in the vibrator is purged with air at a pressure of 0.05 MPa (0.5 kg/cm2G), and the pressure is increased to (2–3 kg/cm2) or 0.2–0.3 MPa in order to dry the interior of the vibrator. (3) Inject 18–20 ml of the standard solution into the vibrator, being careful to prevent bubbles from entering the area in question. First, remove the plugs from the standard solution injection ports (two) fixed on the detector base. Secondly, use a syringe to inject the standard solution into the injection port, so that the solution flows down along the wall of the vibrator tube; it is recommended to use an injection port located near the sampling inlet. If the syringe is dirty, clean it with alcohol. (4) Read the measured value at the reference temperature, which is displayed when the mode selection switch 3 is set to “DSPL” and no function code is shown. (5) If tested twice with standard liquids, blow out the standard liquid used by the vibrator; before purging, seal both injection ports and purge them with the air mentioned in (2). (6) Performing the operations in (3) and (4) yields the same result as that in (4). Note: If the result is different from (4), repeat the steps in (3) and (4). (7) For the calculation of calibration solution 1, press the ’SET’ key when the function number is ‘6’; during the calculation, ‘CAL-1’ flashes, and the density at the reference temperature is displayed after the calculation is completed. (Note 1): Check whether this value is the accurate density of Standard Solution 1. (Note 2. ) Note 1: The verification calculation time varies depending on the density values before and after verification; the greater the difference, the longer the time required. Note 2: The density values after verification do not all match those of the standard solution 1 at the same temperature. Moreover, when there is a large difference between the solution temperature and the reference temperature during verification, errors often occur. However, the error is usually within the acceptable range; if the error is too large, the various setting values need to be checked. (8) Complete the first verification through (7), and then, following the same steps as for the first verification, conduct the second test using standard solution 2. Repeat steps (1) to (7); for the verification calculation setting, set the function code to ‘A’ (CAL—2), and it will flash 7 times. After completing the second verification step, blow out the standard solution in the vibrator and plug the injection port with a blind plug; fully close the needle valves “NV2” and “NV3”, and remove the air connection tube. 4.4.2 Verification using sampled liquid (1) Measure the density of the sampled liquid with a hydrometer; sampling should be carried out only when the liquid density is stable. Note: The density of the liquid being sampled must not change between sampling and the completion of the first calibration step. (2) Measure the density using a densitometer and measure the temperature of the sampled liquid. If Hai is unable to determine the temperature coefficient, the density at high temperatures (reference temperature + about 5°C) and the density at low temperatures (reference temperature – about 5°C) shall be used. The temperature coefficient is calculated using the following formula: Temperature coefficient (g/cm3/°C) = (Density at high temperature – Density at low temperature) / (High temperature – Low temperature). Note: The density must be one that can correspond to the reference temperature. (3) Set the conversion switch of the converter to “CAL”, and enter the data corresponding to function numbers 3, 4, and 5. (4) For the specified first verification calculation, select function number ‘6’ and press the “SET” key. During the calculation period, use “CAL-1”; after the calculation, the density at the reference temperature is displayed. It can be confirmed that this density value is almost identical to that measured in (2). For step (5), prior to changing the density of the solution measured by the sampling unit for the second verification, complete the operation steps from (1) to (4). In the corresponding step (3), enter data for function numbers 7, 8, and 9; in the corresponding step (4), use function number ‘A’ to carry out the verification calculation. 4.4.3 Verification Error: An error message is displayed after the verification calculation (E005 for the first verification, E006 for the second). Check the data entered for function numbers 3, 4, 5, 7, and 8 and recalculate using the correct data. 4.5 Operations 4.5.1 Procedure Start up the density measurement system and check whether the operating conditions are normal. It is not advisable to adjust the measurement system during operation, while routine checks of liquid flow rate and pressure are advisable. Do not heat the detector when the sampling unit is equipped with a vapor heat pipe. If an error message is displayed, it indicates interference; the list of errors is shown in Table 4.2. The errors for E001, 002, 003, and 007 are temporarily canceled by pressing the function number key during maintenance or calibration. And the error prompt for the measurement method is displayed again; these errors are only detected during the measurement process. E005 and 006 occur during the verification process, and are displayed after the calculation is completed and cleared. After that, the density at the pre-verified reference temperature is displayed. Table 4.2 Error List shows Content, Error Resolution, and Handling: E001 – Abnormal detector density signal; identify and eliminate the cause of the fault. E002 – Abnormal detector temperature signal; identify and eliminate the cause of the fault. E003 – Abnormal converter. E004 – Measured temperature out of range. E005 – Abnormality in the first verification step; check and re-enter the data required for verification. E006 – Abnormality in the second verification step. E007 – Error in E2ROM data; check and re-enter the constants. 4.5.2 Checking the measured density value: It is recommended to check the measured density value every few weeks in order to determine the cycle for verification and cleaning. (1) Compare the density measured with a hydrometer with the reading of the vibrating densitometer (density at the reference temperature); when sampling the liquid, ensure that the pressure and temperature are not too different from normal conditions. (2) Correctly measure the density at a reference temperature identical to that of the liquid temperature. (3) Compare the density measured in (2) with the displayed value of the sampled liquid; if the difference exceeds the allowable range, clean the vibrator. Refer to Section 5.1.1 for the cleaning procedure. 4.5.3 Shutdown When stopping sampling according to the following steps, the vibratory density meter should also be shut down, and the sampling liquid in the detector must be drained. 5. Maintenance 5.1 Routine inspection/maintenance 5.1.1 Cleaning the vibrator of the densitometer Dirty particles accumulate on the inner wall of the vibration tube; this is a natural phenomenon associated with flowing liquids and can also cause errors. Clean the pipes in the following manner and at the specified time. (1) Close ball valve “BV1” and needle valves “NV4”, and open needle valves “NV2” and “NV3”. (2) Connect an air tube to the outlet of needle valve “NV2”, and use air at 0.05 MPa (0.5 kg/cm2G) to sweep the sampling liquid in the vibrator from the outlet of needle valve “NV3”. (3) Remove the plugs from the injection ports of the two standard solutions and inject 200 ml of cleaning liquid into the vibrator. (4) After a while, reseal the injection port with a plug, and as described in (2), suction the cleaning liquid from the vibrator; then clean the inside of the vibration tube using the brush (attached) as shown in the figure. (5) Remove the plug from the standard solution injection port again and inject about 200 ml of cleaning liquid. After a short while, reinsert the plug into the port and use air at a pressure of 0.5 kg/cm2G to draw out the sample liquid. Once the liquid has been drawn out, increase the pressure to 0.2–0.3 Mpa (2–3 kg/cm2G) using air in order to dry out the interior components. 5.1.2 Replacement of the detector desiccant. Use desiccants to protect the oscillator amplifier of the detector from moisture, and check the primary and secondary wiring of the detector once a year. If moisture is detected, replace the desiccant; Fujian provides two packs of desiccant. For explosion-proof detectors, before removing the junction box, it is necessary to use a gas detector to check for the presence of explosive gases before opening the box cover. 5.2 Check and troubleshoot faults. Maintaining a vibrating densitometer requires experience; adjustments must be made after replacing the files. In the event of a failure, per the regulations, Yokogawa Company is responsible for carrying out the repairs, which allows the fault to be resolved effectively and quickly. The fault inspection method is as follows: For explosion-proof detectors, before removing the cover of the wiring box, it is necessary to use a gas detector to check for the presence of anti-explosion gases before opening the box cover. Remove the cover of the detector, observe the vibrator, and carefully inspect the entire cross-section of the two cylindrical vibration tubes. If there are defects, such as scratches or other visible marks that cause leakage of the sampled liquid, then the vibration tube needs to be replaced. (Note) Do not let the fixing screws collide with the vibrator. Note: The vibrator is made of very thin-walled tubes, so care must be taken when handling it, as installing and removing the vibration tube requires special skills; it must be replaced by Yokogawa Corporation. 5.2.2 Check the resistance between the RTD measurement terminals A2 and A3. When the RTD is functioning properly, the other resistance values are as shown in Table 5.1: Resistance of RTD at various temperatures (Pt1000). Temperature (°C): 10, 15, 20, 25, 30, 35, 40, 45, 50; Resistance (Ω): 1039.0, 1058.5, 1077.9, 1097.3, 1116.7, 1136.1, 1155.4, 1174.7, 1194.0. 5.2.3 Check the oscillation amplifier. First, examine the capacitive sensing electrodes; these electrodes must be installed in the small gaps between the vibration tubes. Without this gap, the electrode cannot function properly. If there are dirty objects or moisture between the vibration tube and the electrode, clean the gap using a cloth, being careful not to damage the vibrator. Then, check the electronic circuit using a DC voltmeter and similar instruments, regarding the instrument numbers and inspection points. See the figure. This post was last edited by chengjingbao on 2009-4-5 at 17:31.]