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HART Protocol Intelligent Pressure Transmitter Features And Selection Techniques

Jan 11, 2019

HART protocol intelligent pressure transmitter features and selection techniques

HART protocol intelligent pressure transmitter is assembled with various sensor chips (diffused silicon, ceramic capacitor) components and high-quality integrated circuits. It has high quality, low price and can adapt to various industrial applications. Advanced circuit technology materials, sealed and solidified from the outside, can meet the requirements of moisture-proof, waterproof, explosion-proof, anti-corrosion, dust-proof and other harsh working conditions. Different process connecting parts can be used for strong rot medium, high and low temperature medium, and sticky. Accurate measurement of thick media.

Main feature:

(1) Output and communication

Communication via the HART protocol allows output and communication to occur simultaneously without compromising loop integrity. When RS485 communication is selected, data and configuration data can be transmitted through the RS485 port.

(2) Data storage (smart type)

The configuration data is stored in non-volatile EEPROM memory on the transmission board. The data can still be saved after the transmitter is powered off, so the transmitter can work immediately when it is powered on.

(3) Digital/analog conversion and signal transmission (smart type)

Process quantities are stored in digital data for linear correction and engineering unit conversion

(4) Configuration software function

The HART protocol makes it easy for users to configure, test and configure intelligent pressure transmitters, or to communicate via any host computer that supports the HART protocol.

(5) Failure continuous self-test

Intelligent industrial pressure transmitters for continuous self-testing. If a problem is found, the transmitter activates the user-selectable analog output alarm.

HART protocol intelligent pressure transmitter features and selection techniques

Industrial pressure transmitter selection tips:

1. What kind of pressure should the transmitter measure?

First determine the large ZUI value in the system to confirm the measured pressure. In general, you need to select a transmitter with a pressure range that is about 15 times larger than the ZUI value. This is mainly in many systems, especially in water pressure measurement and processing, with peak and continuous irregular up and down fluctuations, which can damage the pressure sensor, continuous high pressure value or slightly beyond the transmitter. Calibrating large values of ZUI will shorten the life of the sensor, however, this will result in reduced accuracy. Thus, a buffer can be used to reduce the pressure glitch, but this will reduce the response speed of the sensor. Therefore, when selecting a transmitter, it is necessary to fully consider the pressure range, accuracy and stability.

2. What kind of pressure medium:

What we need to consider is the medium measured by the pressure transmitter. The viscous liquid and mud will block the pressure interface. The solvent or corrosive substances will not damage the material that is directly in contact with these media. These factors will determine whether to choose a direct barrier and a material that is in direct contact with the media. The contact medium part of the general pressure transmitter is made of 316 stainless steel. If your medium is not corrosive to 316 stainless steel, then basically all pressure transmitters are suitable for measuring the medium pressure. If your medium Corrosive to 316 stainless steel, then we must use a chemical seal, which not only can measure the pressure of the medium, but also effectively prevent the medium from contacting the liquid contact part of the pressure transmitter, thus protecting the pressure transmission. Extends the life of the pressure transmitter

pressure transmitter

3. How much accuracy does the transmitter need?

Determining the accuracy, nonlinearity, hysteresis, non-repetitiveness of the electromechanical business network, temperature, zero offset scale, temperature effects. But mainly by nonlinearity, hysteresis, non-repetition, the higher the accuracy, the higher the price. Each type of electronic measuring instrument will have accuracy error, but the accuracy level of each country is different. For example, the accuracy of national standards such as China and the United States is a good part of the sensor's online degree ZUI, which is what we usually do. Say the accuracy of the measurement range between 10% and 90%; and the accuracy of the European standard is the worst part of linearity, which is what we usually call 0 to 10% and 90% to 1 0 0 The accuracy between %, such as the European standard, is 1%, and the accuracy of the Chinese standard is 0.5%.

4, The temperature range of the transmitter:

Usually one transmitter will calibrate two temperature ranges, the temperature range for normal operation and the temperature compensateable range. The normal operating temperature range refers to the temperature range when the transmitter is not damaged during operation. When the temperature is outside the range, the performance index of the application may not be achieved. The temperature compensation range is a typical range that is smaller than the operating temperature range. Working within this range, the transmitter will definitely achieve its performance specifications. Temperature changes affect its output in two ways, one is zero drift; the other is affecting full-scale output. For example: +-X% °C of full scale, +/-% °C of reading, +/-×% of full scale over temperature range, +}-X% of reading within temperature compensation range, if not These parameters lead to uncertainty in use. The change in the output of the transmitter is caused by a change in pressure or by a change in temperature. Temperature effects are the most complex part of understanding how to use the transmitter.

5. What kind of output signal is needed:

For miv, V, mA, and frequency output digital inputs, the choice of which input depends on a number of factors, including the distance between the transmitter and the system controller or display, and the presence of noise or other electronic interference signals. Whether the amplifier, the position of the amplifier, etc. are required. For many devices with short distances between transmitter and controller, the most economical and effective solution for mA output transmitters, if you need to amplify the output signal, ZUI uses a transmitter with built-in amplification. For long-distance transmission or strong electronic interference signals, it is best to use mA-level transmission or frequency transmission. In the case of RF or EM indicators that are very embarrassing, in addition to paying attention to the choice of mA or frequency output, special protection or filters should be considered. (At present, due to the needs of various acquisitions, there are many kinds of output signals of pressure transmitters on the market, mainly 4.20mA.20mA, 0.10V0.5, etc., but the more common ones are 4.20mA and 0.10. Among the output signals I mentioned above, only 4.20mA is a two-wire system. The output we have said is that the wire system does not contain grounding or shielding wires, and the others are three-wire system.

6. What kind of excitation voltage is selected:

The type of output signal determines how the excitation voltage is selected. Many amplification transmitters have built-in voltage regulation, so the power supply voltage range is larger. Some transmitters are quantitatively configured and require a stable operating voltage. Therefore, a working voltage can be obtained to determine whether or not to use a regulator. When selecting a transmitter, the sensor must consider the operating voltage and system cost.

differential pressure transmitter

7. Do you need an interchangeable transmitter:

Determine if the required transmitter can accommodate multiple operating systems. Generally speaking, this is very important. Especially for OEM products. Once the product is delivered to the customer, the cost of the customer's calibration is considerable. If the product has good interchangeability, even if the transmitter used is changed, it will not affect the effect of the whole system.

8, The transmitter needs to maintain stability after working overtime

Most transmitters will “drift” after a timeout, so it is important to understand the stability of the transmitter before purchasing. This pre-work can reduce the hassle of future use.

9, The package of the transmitter:

The package of the transmitter, especially often overlooked, is its frame, however this will gradually reveal its shortcomings in later use. In the purchase of the transmitter must take into account the future working environment of the transmitter, how the humidity, how to install the transmitter, there will be strong impact or vibration.

10. What kind of connection is used between the transmitter and other electronic devices:

Is it necessary to use a short-distance connection? If a long-distance connection is required, is it necessary to use a connector?

11, Other:

After confirming some of the above parameters, we must also confirm the process connection interface of your pressure transmitter and the supply voltage of the pressure transmitter; if it is used in special occasions, the explosion protection and protection level should also be considered.