How to select a pressure transmitter

To ask this question, you don’t even understand the concepts of these three things; how can you talk about choosing one over the others?

Well, then I’d appreciate it if you could explain it simply. I’m new to this topic, and I seem to not be able to understand the information available online. Could you make it easier to understand?

It’s like asking when exactly to eat bread, steamed buns, rolls, or rice It’s not easy to explain. You can look it up on Baidu for the basic stuff.

This process design will be proposed to you; it’s their decision, but you can review whether what they propose is reasonable. What matters most is who to install it from and who to buy it from.

Generally speaking, this is chosen based on the operating conditions

Send your parameter list to the transmitter manufacturer; they will select the appropriate ones for you, and then once you see the samples you’ll know everything! :lol

On the 4th floor, the concepts of gauge pressure, absolute pressure, and negative pressure were explained. Based on these concepts, it is sufficient to have a thorough understanding of the physical properties of the medium being measured as well as the environmental conditions, such as the medium’s temperature, pressure range, degree of corrosion, whether it is single-phase or multi-phase, the installation method (vertical or horizontal), the electromagnetic conditions in the environment, temperature, the distance over which power is transmitted, whether the installation is outdoors or indoors, as well as the accessories of the transmitter (terminal blocks, valve assemblies). For differential pressure, it depends on whether it is used to measure liquid level, flow rate, or the differential pressure across process equipment, etc. Ask experienced craftsmen for advice more often, and learn more about the basic knowledge of instruments; your skills will improve quickly.

A pressure transmitter mainly consists of three components: a pressure-sensing element sensor (also known as a pressure sensor), a measurement circuit, and process connections. It can convert the physical pressure parameters of gases, liquids, etc., detected by the pressure-sensing element, into standard electrical signals (such as 4–20 mA DC), which are then supplied to secondary instruments such as indicator alarms, recorders, and regulators for measurement, indication, and process control. When selecting a pressure transmitter, the following points can serve as a guide: 1. What is the type of pressure medium? Viscous liquids and mud can clog the pressure interface, while solvents or corrosive substances may damage the materials in the transmitter that come into direct contact with these media. These factors will determine whether to choose a direct isolation film and materials in direct contact with the dielectric. 2. What level of precision is required for the transmitter? Factors that determine precision include non-linearity, hysteresis, non-repeatability, temperature, zero-point offset, and the influence of temperature. But due mainly to non-linearity, hysteresis, and non-repeatability, the higher the precision, the higher the price. 3. What type of pressure is the transmitter intended to measure? First, determine the maximum pressure value in the system; generally, it is necessary to choose a transmitter with a pressure range that is about 1.5 times greater than this maximum value. This is mainly because in many systems, especially those involved in pressure measurement and processing, there are peak values as well as continuous irregular fluctuations; such sudden peaks can damage pressure sensors. Sustained high pressure levels or values slightly above the transmitter’s calibrated maximum can shorten the sensor’s lifespan, and it also reduces accuracy. Therefore, a buffer can be used to reduce pressure spikes, but this will slow down the sensor’s response time. Therefore, when selecting a transmitter, the pressure range, accuracy, and stability must be taken into full consideration. 4. As for what type of output signal is required—mV, V, mA, or digital output at a certain frequency—the choice of output depends on various factors, including the distance between the transmitter and the system controller or display, the presence of \"noise\" or other electronic interference signals, whether an amplifier is needed, and the location of the amplifier. For OEM devices where the distance between many transmitters and controllers is short, transmitters with mA output represent the most economical and effective solution. 5. Temperature range of the transmitter: Typically, a transmitter is calibrated for two temperature ranges. One of these ranges is the normal operating temperature, while the other is the temperature compensation range. The normal operating temperature range refers to the temperature range within which the transmitter can function without being damaged; outside this temperature compensation range, it may fail to meet the required performance specifications. The temperature compensation range is a typical range that is smaller than the operating temperature range. Operating the transmitter within this range will definitely ensure that it meets its intended performance specifications. Temperature affects its output in two ways: one is zero drift, and the other is an impact on the full-scale output. For example: +/-X%/℃ of full scale, +/-X%/℃ of the reading, +/-X% of full scale when outside the temperature range, +/-X% of the reading within the temperature compensation range; the absence of such parameters leads to uncertainty in use. The change in the transmitter output is caused by pressure changes or by temperature changes. The effect of temperature is the most complex part when understanding how to use transmitters. If it is necessary to amplify the output signal, it is best to use a transmitter with built-in amplification. For long-distance transmission or in the presence of strong electronic interference signals, it is best to use mA-level output or frequency output. In environments with high RFI or EMI levels, in addition to choosing mA or frequency output, it is also necessary to consider special protection measures or filters. 6. What excitation voltage to choose: The type of output signal determines which excitation voltage should be selected. Many transmitters have built-in voltage regulation circuits, which allows for a wide range of supply voltages. Some transmitters are configured for fixed quantities and require a stable operating voltage; therefore, the operating voltage determines whether to use sensors with regulators. When selecting a transmitter, both the operating voltage and the system cost must be taken into consideration. 7. Is a interchangeable transmitter required? Determine whether the desired transmitter can be used in multiple systems. Generally speaking, this is very important, especially for OEM products. Once the product reaches the customer, the cost incurred by the customer for calibration is quite high. If the products have good interchangeability, then even changing the transmitters used will not affect the performance of the entire system. 8. Transmitter enclosure: The enclosure of the transmitter – its housing – is often overlooked, yet its shortcomings will become apparent over time as it is used. When selecting a transmitter, it is essential to take into account the future operating environment of the transmitter, such as the humidity levels, how it will be installed, and whether there will be any severe impacts or vibrations. 9. Transmitters need to maintain stability after operating for an extended period. Most transmitters experience \"drift\" after being used beyond their intended limits; therefore, it is essential to understand the stability of a transmitter before purchasing it. Such prior assessment can help avoid various problems that may arise during future use. 10. What kind of connection should be used between the transmitter and other electronic devices?