4-20mA Hart protocol for intelligent differential pressure transmitter for fire equipment pressure difference detection

1、 Instrument Overview:

Intelligent differential pressure transmitter is a new type of transmitter produced by introducing advanced foreign technology and equipment. The key raw materials, components, and components are all imported. The entire machine has undergone strict assembly and testing, and has the characteristics of advanced design principles, complete variety and specifications, and easy installation and use.

2、 Measurement principle:

Intelligent differential pressure transmitter is a device that operates when two types of pressures of the measured medium are introduced into the high and low pressure chambers, acting on the δ On both sides of the isolation diaphragm of the component (i.e. sensitive component), the filling liquid inside the component is transmitted to both sides of the measurement diaphragm through the isolation diaphragm. Measure the membrane and the electrodes on both sides of the insulation sheet to form a capacitor. When the pressure on both sides is not equal, it causes displacement of the measuring diaphragm. The displacement is proportional to the pressure difference, so the capacitance on both sides is not equal. Through oscillation and demodulation, it is converted into a signal proportional to the pressure.

3、 Applicable occasions:

Differential pressure transmitters are used to measure the liquid level, flow rate, and pressure of liquids, gases, or vapors in high working pressure environments, and then convert them into 4-20mA DC signal outputs. The intelligent type can communicate with the HART manual operator to set, monitor, or form an on-site monitoring system with the upper computer.

4、 Performance characteristics:

1. Super measurement performance for pressure, differential pressure, liquid level, and flow measurement;

2. Digital accuracy:+(-) 0.2%;

3. Stability: 0.25% for 60 months;

4. Range ratio: 100:1;

5. Measurement rate: 0.2S;

6. Miniaturized (2.4kg) all stainless steel flange, easy to install;

7. Process connection is compatible with other products to achieve measurement;

8. The sensor (technology) with H alloy sheath achieves excellent cold and hot stability;

9. Differential pressure transmitter using a 16 bit computer;

10. Standard 4-20mA with digital signal based on the HART protocol.

5、 Technical indicators:

1. Objects of use: liquids, gases, and vapors;

2. Measurement range: -6-6MPa (customizable within the range);

3. Output signal: 4-20mADC (two wire system)

4. Power supply: 12-45VDC, usually 24VDC;

5. Load characteristics: related to the power supply, carrying load capacity at a certain power supply voltage; The relationship between load impedance RL and power supply voltage Vs is: RL ≤ 50 (Vs-12);

6. Indicator: LCD liquid crystal display;

7. Explosion proof grade: Intrinsically safe (Exia II BT6);

8. Range and zero point: continuously adjustable externally.

6、 Fault diagnosis:

During the measurement process of transmitters, some faults often occur. Timely diagnosis, analysis, and handling of faults are crucial for ongoing production. We have summarized and summarized some judgment and analysis methods and processes based on our experience in daily maintenance.

1. Investigation method:

Review the incidents of ignition, smoke, odor, power supply changes, lightning strikes, humidity, incorrect operation, and maintenance before the fault occurred.

2. Intuitive method:

Observe the external damage of the circuit, leakage of the pressure pipe, overheating of the circuit, and the status of the power supply switch.

3. Detection method.

a. Open circuit detection: Separate the suspected faulty part from other parts to see if the fault has disappeared. If it does, determine the location of the fault. Otherwise, proceed to the next step of investigation. For example, if the intelligent differential pressure transmitter cannot communicate remotely with Hart, the power can be disconnected from the instrument body and the transmitter can be powered on for communication by adding an additional power source on site, To check if the cable is interfering with communication due to an electromagnetic signal of approximately 2kHz superimposed on it.

b. Short circuit detection: Under the premise of ensuring safety, directly short circuit the relevant circuits. For example, if the output value of the differential pressure transmitter is too small, the pressure pipe can be disconnected, and the differential pressure signal can be directly led to both sides of the differential pressure transmitter from outside the primary pressure valve. Observe the output of the transmitter to determine the connectivity of the pressure pipeline for blockage or leakage.

c. Replacement detection: Replace the suspected faulty parts and determine the faulty location. If it is suspected that the transmitter circuit board has malfunctioned, a temporary replacement can be made to determine the cause.

d. Partial inspection: Divide the measurement circuit into several parts, such as power supply, signal output, signal transmission, and signal detection. Conduct inspection in parts, from simple to complex, from surface to interior, to narrow the scope and identify the fault location.

7、 Installation requirements:

1. Before installation, please carefully read the product manual and verify the relevant information of the product.

2. The transmitter should be installed in a ventilated, dry, corrosion-free, and cool place. If installed outdoors, a protective cover should be added to avoid sunlight and rain, and to avoid performance degradation or malfunction of the transmitter.

3. Transmitters are precision instruments, and should not be subjected to strong impacts or falls during installation.

4. Connect correctly according to the wiring diagram.

5. Pay attention to protecting the outgoing cables of the transmitter. When used in industrial sites, it is recommended to use metal pipes for protection or overhead. Do not loosen the sealing nut at the cable outlet to prevent moisture from entering.

8、 When using a differential pressure transmitter, the following three points should be noted:

1. The differential pressure transmitter must be recalibrated for its measurement range, zero drift, accuracy, static pressure error, etc. before use.

2. After the installation of the transmitter, it is also necessary to check the working pressure, working temperature, measurement range, drift amount, etc. of various transmitters before driving. Check if it matches the actual situation. If there are any discrepancies, the cause must be identified and corrected before driving.

3. When starting and stopping, the instrument should avoid being subjected to unidirectional static pressure.