Pressure transmitters and temperature transmitters are both commonly used industrial measuring instruments. Although they look almost the same, there is still a big difference in performance and structure. In this paper, we mainly introduce the difference between pressure transmitters and temperature transmitters from five aspects in detail.
1.Concept
A pressure transmitter is a pressure converted into pneumatic or electric signals for control and remote transmission of equipment, mainly by the pressure element sensor, module circuit, display head, case and process connectors, and so on. It can convert the physical pressure parameters of gas and liquid sensed by the pressure measuring element sensor into standard electrical signals (e.g., 4-20mADC, etc.), which can be supplied to secondary instruments such as indicator alarms, recorders, and regulators for measurement, indication, and process adjustment. Pressure transmitter is divided into absolute pressure transmitter, differential pressure transmitter, surface pressure transmitter, and other types.
Temperature transmitter uses a thermocouple, RTD as the temperature measurement element, the output signal from the temperature measurement element is sent to the transmitter module, after regulator filtering, operational amplification, nonlinear correction, V/I conversion, constant current, and reverse protection circuit processing, converted into a linear relationship with the temperature of the 4 ~ 20mA current signal 0-5V/0-10V voltage signal, RS485 digital signal output. A temperature transmitter is generally divided into two types, including RTD and thermocouple type. Temperature transmitter has the advantages of simple structure, lead saving, large output signal, strong anti-interference ability, good linearity, simple display instrumentation, solid module seismic moisture, reverse connection protection and current limiting protection, and reliable operation.
2.Working Principle
The working principle of a pressure transmitter is to convert the measured pressure into a standard electrical signal output. In the industrial automation control system, these signals are used to monitor and control parameters. Pressure transmitters to feel the pressure of the electrical components are generally resistance strain gage, resistance strain gage is a kind of pressure that will be measured on the piece of conversion into an electrical signal-sensitive device. Resistive strain gauges are most commonly used as metal resistive strain gauges and semiconductor strain gauges. There are two types of metal resistive strain gauges: filament strain gauges and foil strain gauges. Usually, the strain gauge is tightly bonded to the mechanical strain substrate through a special adhesive. When the substrate is subjected to stress changes, the resistance strain gauges will also deform together to change the resistance value of the strain gauges, which will change the voltage added to the resistance.
The temperature transmitter is an instrument that converts the measured temperature into a standard electrical signal output. The working principle of the temperature transmitter is based on the thermoelectric effect. The thermoelectric effect is the difference in electrical potential that occurs at the point of contact of two different metals because of the temperature difference. The temperature transmitter is generally composed of two different metal thermocouples or RTD sensing elements and the measured temperature point is connected to form a thermoelectric circuit. When the measured temperature changes, the temperature in the thermoelectric circuit also changes. The thermocouple or RTD sensing element generates a weak electrical signal related to the temperature. The temperature transmitter collects and amplifies this weak signal and converts it into a standard current or voltage signal. Temperature transmitters are generally equipped with amplification and linearization circuits inside to enhance and adjust the signal output from the sensor. The amplification circuit can amplify weak signals to a suitable range for subsequent data processing and transmission. The linearization circuit, on the other hand, is capable of correcting the non-linear temperature-voltage or temperature-current characteristics to ensure an accurate correspondence between the output signal and the measured temperature. In short, the temperature transmitter is a kind of temperature-measuring instrument based on the thermoelectric effect, through the acquisition, amplification, and conversion of the output signal of the temperature-sensitive element, the temperature information will be converted into a standard signal for transmission and processing.
3.Field of Application
Pressure transmitter is one of the most commonly used sensors in industrial practice, which is widely used in a variety of industrial self-control environments, involving water conservancy and hydropower, ships, pipelines, railroad transportation, production automation, petrochemical, oil wells, electric power, machine tools, and many other industries. It is mainly used to measure and control the pressure and flow parameters of pipelines, containers, pumps, etc., in order to realize precise control of the production process and ensure the safety and stability of the production line.
In contrast, the application of temperature transmitters is more extensive. Not only can play a role in the field of industrial automation measurement and control, but also widely used in heat treatment, refrigeration, heating, thermodynamic experiments, and medical and other fields. It is especially suitable for computerized measurement and control systems, and can also be used in conjunction with instruments.
4.Performance Parameters
The main performance parameters of the pressure transmitter include range, accuracy, output signal, etc., while the main performance parameters of the temperature transmitter include measurement range, accuracy, response time, output signal, etc. The two performance parameters are different. The performance parameters of the two are different, so when choosing and using them, you need to consider them according to different practical needs.
5.Applicable Environment
Due to different operating principles and applications, pressure and temperature transmitters differ in their respective environments. Pressure transmitters are suitable for low temperature and low relative humidity environments. The pressure transmitter can adapt to the ambient temperature is generally -10 ~ 55 degrees Celsius, and the reference working conditions of 20 ± 5 degrees Celsius; when the ambient temperature deviation from the reference working conditions, will produce thermal zero and thermal sensitivity drift. The temperature transmitter can be applied to high temperatures, corrosion and vibration, and other harsh environments.
Summarize
In summary, pressure transmitters and temperature transmitters differ greatly in their operating principles, application scenarios, performance parameters, and applicable environments. In the actual use of the process, the choice of the appropriate type of transmitter and parameters of industrial automation control has an important impact on stability and accuracy.