Safety barrier maintenance and repair procedures

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Safety Barrier Maintenance and Repair Procedures 1 General Provisions 1.1 Subject Matter and Scope of Application These procedures specify the specific technical requirements and implementation steps for the maintenance, repair, commissioning of safety barriers, as well as the safety precautions to be observed. These regulations apply to the DAB type input and output safety barriers of the DDZ-III electric unit combination instruments used online in chemical processing plants (hereinafter referred to as the instruments); the DFA type safety barriers should also be used with reference to these regulations. 1.2 Basic working principle: This instrument operates on the principles of electromagnetic isolation and energy limitation. 1.3 Composition and Function The composition of this instrument is shown in Figures 1 and 2. Figure 1 shows an input-type instrument, while Figure 2 shows an output-type instrument. The I/I isolation conversion circuit isolates and converts the 4–20mA current signal from a transmitter or regulator into a 4–20mA or 1–5V voltage signal for output, with a conversion factor of K=1. The energy limitation circuit limits the current and voltage entering the hazardous area to within the rated values. The DC/AC conversion circuit converts the 24VDC power supply into a power source that powers the current-limiting circuit and the I/I conversion circuit. 1.4 Main Technical Performance and Specifications 1.4.1 Performance Indicators Basic error: ±0.2% for input type, ±0.5% for output type. Hysteresis error: 0.2% for input type, 0.5% for output type. Power limit setting: Current rating < 35mA; Voltage rating < 35V DC. Supply voltage range: 18.5–28.5V DC. Insulation resistance: >100MΩ. 1.4.2 Specifications Input signal: 4–20mA. Output signal: 4–20mA or 1–5V DC for input type; 4–20mA for output type. Power supply: 24V DC ±5%. Ambient temperature: 0–40°C. Relative humidity: ≤85%. 1.5 Basic Requirements for Maintenance Personnel Maintenance personnel should meet the following requirements: a. Be familiar with these regulations, as well as the corresponding product manuals and other relevant technical documents ； b. Understand the process flow and the role of this instrument within it ； c. Master the basic theoretical knowledge in areas such as mathematical fundamentals, electrical engineering fundamentals, and electronic engineering fundamentals ； d. Master the basic skills of instrument maintenance, repair, commissioning, and handling of common faults ； e. Master the usage of common testing instruments and relevant standard instruments. 2 Intact conditions 2.1 The components are complete and meet the technical requirements, namely: a. The nameplate should be clear and error-free ； b. The components should be in good condition, complete, and standardized ； c. Fasteners must not be loose ； d. The moving parts should be flexible ； e. The terminal connections should be secure ； f. The adjustable parts should be in the position of the adjuster. 2..2 It operates normally and meets the usage requirements, namely: a. During operation, the instrument should achieve the specified performance indicators ； b. Under normal conditions, the energy conversion element does not experience an excessive temperature rise. 2.3 The equipment and the surrounding area should be neat and clean, meeting the requirements for work; that is: a. The entire unit should be clean, free from rust, with a smooth and shiny paint finish without any peeling ； b. The instrument wiring is neatly laid out ； c. The line numbers are complete, clear, and accurate ； d. There should be no corrosive gases around the instruments. 2.4 The technical documents are complete, accurate, and meet the management requirements, that is: a. The instruction manuals, certificates of conformity, and inspection certificates upon arrival at the factory must be available ； b. Operation records, fault handling records, maintenance records, and parts replacement records must be accurate ； 3 Maintenance 3.1 Routine Maintenance 3.1.1 Patrol Inspections At least two patrol inspections shall be carried out per shift, with the inspection contents including ； a. Consult the on-duty process personnel regarding the operation of the instruments. b. Check whether the power supply to the instruments is functioning properly ； c. Check whether there is any leakage, damage, or corrosion in the table body ； d. Any issues identified should be addressed promptly, and 3.1.2 Regular maintenance must be carried out. The tasks included in regular maintenance are: a. Clean the exterior of the instruments once per shift ； b. A check of the basic error should be performed every 6 months. 3.2 Regular calibration 3.2.1 Calibration interval The calibration interval is 12 months. 3.2.2 Calibration instruments Digital voltmeter: 0.05 grade Standard resistance box: 0.02 grade Precision resistors: 0.01 grade, 250Ω; 0.01 grade, 10Ω Current signal generator: 0–20mA Megohmmeter: 500V DC regulated power supply: 0–40V ±1% 3.2.3 Standard wiring The standard wiring is shown in Figures 3 and 4. Figure 3 shows the wiring diagram for calibrating input-type instruments, while Figure 4 shows that for output-type instruments. 3.2.4 Calibration of basic error At least 5 equal division points should be used for calibration. Turn on the power supply and allow it to warm up for 15 minutes. Slowly increase the input signal, applying the signal values at each calibration point one after another, and read the values displayed on the digital voltmeter ； Then reduce the value of the input signal, and perform reverse calibration on the instrument using the same method; if the error exceeds the allowable value, adjust the zero potentiometer and the range potentiometer until the result is satisfactory. 3.2.5 Backward error calibration: The backward error calibration is carried out simultaneously with the basic error calibration, and its maximum backward error shall not exceed the allowable value. 3.2.6 Power Limit Performance Calibration The calibration wiring is shown in Figure 5. As the DC regulated voltage source is gradually increased from 24V to 40V, the reading on the digital voltmeter represents the highest open-circuit voltage value. Connect a 1Ω resistor to the safety spark-type terminals that link the field instruments; then gradually increase the voltage of the DC regulated supply from 24V to 40V. The voltage value across the 1Ω resistor, as measured by the digital voltmeter, can be used to determine the maximum short-circuit current value. 3.2.7 Voltage range calibration: The standard wiring is shown in Figure 6. Adjust the voltage to 25.2 V, and tune the resistor box so that the input current signal is 4 mA; use a digital voltmeter to measure the voltage at the input terminal ； Then adjust the supply voltage to 22.8V, and tune the resistor box so that the input current is 20mA. Use a digital voltmeter to measure the voltage at the input terminal; the two measured voltage values represent the range of the distribution voltage. 3.2.8 Insulation resistance check: Use a megohmmeter with a rated DC voltage of 500V to measure the insulation resistance values from the input terminal, output terminal, and power supply terminal to ground. 3.2.9 Calibration quality standards: The calibrated instruments shall meet the performance specifications specified in Article 1.4.1. 3.3 Faults and Troubleshooting Common faults and troubleshooting methods for input and output instruments are shown in Table 1. Phenomenon, Cause, Treatment Method: No signal output; Output connection broken; Connect the connection; CH1 is open-circuited or D9.D10.D11.D12 are damaged, resulting in abnormal voltage; Connect CH1 or replace D9.D10.D11.D12; T3.T4.T5.T6 are damaged; Replace T3.T4.T5.T6; No input current; Fuse is blown; Replace the fuse; The DC/AC converter is not working properly; Input circuit connection broken; Check the DC/AC converter and connect the input circuit; The current-limiting circuit is not working properly; Check the current-limiting circuit; Basic error is out of spec; T3.T4.T5.T6 performance has declined; Replace T3.T4.T5.T6; Range potentiometers and zero potentiometers (W1.W2.W3) are in the wrong position; Adjust the position of W1 and use W2.W3 to set the zero point and range; Reverse resistance of D3.D4 has decreased; Replace D3.D4; Inductance of the primary and secondary coils of the current transformer has decreased; Replace the current transformer; The DC/AC converter is not working properly; Check the DC/AC converter; Large output when there is no input current; T3.T4.T5.T6 are damaged; Replace T3.T4.T5.T6; No output signal; Output terminal is open-circuited; Connect the output terminal; Polarity of the input signal terminal is reversed; Connect the input signal correctly; D5.D6.D7.D8 are damaged, causing abnormal voltage at C5; Replace D5.D6.D7.D8; T5.T6 are damaged; Replace T5.T6; The current-limiting circuit is not working properly; Check the current-limiting circuit; No input signal; Input circuit connection broken; Connect the input circuit; T3.T4 are damaged; Replace T3.T4; The DC/AC converter is not working properly; Check the DC/AC converter; Basic error is out of spec; T5.T6 performance has declined; Replace T5.T6; The current transformer is not working properly; Replace the current transformer. Table 1-4 Maintenance 4.1 Maintenance Cycle: This instrument should be maintained every 12 months, usually in conjunction with the factory’s annual maintenance. 4.2 Maintenance Tasks 4.2.1 Remove dust from inside and outside the instruments. 4.2.2 Check all wiring connections to ensure that there are no loose or missing solder joints, and that none of the solder joints are oxidized. 4.2.3 Calibrate the instruments in accordance with Article 3.2 of these procedures. 4.2.4 Check and tighten all fasteners. 4.2.5 Instruments after maintenance shall be calibrated in accordance with the **(Department) Metrological Calibration Procedures. 4.3 Maintenance Quality Standards The instruments after maintenance shall meet the sound condition specified in Chapter 2. 5 Commissioning Preparations before Commissioning 5.1.1 Check whether the power supply for the instruments is normal. 5.1.2 Check whether the wiring is correct and secure. 5.2 Commissioning Steps 5.2.1 Turn on the power to the instrument to put it into operation. 5.3 Acceptance 5.3.1 Check the completion of each maintenance item one by one. 5.3.2 Check whether the instruments meet the maintenance quality standards. 5.3.3 After the instrument has been operating normally for 72 hours, it shall be signed for by the relevant technical supervisor. 6 Safety Precautions 6.1 Precautions for Maintenance 6.1.1 Maintenance must be carried out by two or more persons. 6.1.2 For operations that may cause fluctuations in process parameters, approval from process engineers must be obtained in advance before maintenance is carried out. 6.1.3 If it is necessary to remove the entire movement, the power supply must be turned off first. 6.2 Safety Precautions for Maintenance 6.2.1 A maintenance work order must be filled out for the maintenance of operating instruments.