The fundamental principle of a dp pressure transmitter involves dividing a space into two chambers using a sensitive element (typically a diaphragm). When pressure is applied to each chamber, the sensor undergoes displacement (or a tendency to displace) under the combined effect of both pressures. This displacement is directly proportional to the pressure differential (differential pressure) between the two chambers. This displacement is then converted into a standard output signal that reflects the magnitude of the differential pressure.
Specifically, the pressure of the measured medium acts on the isolation diaphragms in the high-pressure and low-pressure chambers of the dp pressure transmitter. This pressure is transmitted to both sides of the measuring diaphragm through the isolation diaphragms and the filling fluid within the element. The measuring diaphragm and electrodes on both insulating plates each form a capacitor. When pressures on either side are unequal, displacement occurs in the measuring diaphragm, causing capacitance differences between the two sides. Through oscillation and demodulation circuits, this is converted into a signal proportional to the pressure.
Measurement Range: Clearly define the maximum and minimum values of the measured pressure differential. The selected DP Pressure Transmitter's range should be approximately 1.5 times greater than the maximum pressure differential likely to occur in the system. This prevents sensor damage from transient peaks while ensuring sufficient accuracy within the normal measurement range. For example, if the pressure differential in the system fluctuates between 0-100 kPa, a dp pressure transmitters with a range of 150 kPa or higher should be selected.
Medium Properties: Consider the characteristics of the measured medium, such as whether it is a viscous liquid, slurry, or other media prone to clogging pressure ports, as well as its corrosiveness. For corrosive media, select appropriate diaphragms and wetted materials to ensure the transmitter's service life.
Accuracy Requirements: Select an appropriate DP Pressure Transmitter based on the measurement accuracy demanded by the application scenario. Higher accuracy typically comes at a higher cost. A balance between accuracy and cost must be comprehensively considered.
Temperature Range: Understand the transmitter's normal operating temperature range and temperature compensation range to ensure that temperature variations in the actual operating environment do not affect the transmitter's performance or measurement accuracy.
Output Signal: Select an appropriate output signal based on control system requirements, with common options including 4-20mA, 0-5V, and RS485. Simultaneously consider factors such as signal transmission distance and potential electronic interference.
Explosion-Proof Requirements: In hazardous environments with flammable or explosive materials, such as petrochemical plants or coal mines, DP Pressure Transmitters compliant with relevant explosion-proof standards must be selected. This includes flameproof or intrinsically safe transmitters to ensure operational safety.
Installation Method: Select the appropriate installation method based on site conditions and space constraints, such as direct mounting or flange mounting. Ensure the installation location is easily accessible for maintenance and observation, and maintain consistent elevation for the transmitter's “+” and “-” pressure chambers.
(1) Abnormal Output Signal:
Check Power Supply: Verify the transmitter's power supply is functioning correctly, including stable voltage and compliance with operating requirements. Power supply issues may cause unstable or absent output signals.
Inspect Wiring: Examine whether the transmitter's wiring is correct and secure, checking for loose connections, short circuits, or open circuits. Wiring errors or poor contacts can disrupt signal transmission.
Check Sensor: The sensor is the core component of the differential pressure transmitter. Damage or malfunction to the sensor will cause abnormal output signals. You can determine if the sensor is functioning normally by checking parameters such as its resistance or capacitance values.
Check Environmental Factors: Environmental factors like temperature, humidity, and electromagnetic interference may affect the transmitter's performance. For example, high temperatures may reduce the transmitter's accuracy, while electromagnetic interference may cause signal distortion.
(2) Inaccurate Pressure Measurement:
Zero Calibration: Perform zero calibration to ensure the transmitter outputs zero when no pressure differential is present. Zero offset will cause inaccurate measurement results.
Check Pressure Tubing: Inspect the pressure tubing for blockages, leaks, or air bubbles. Issues with the tubing can disrupt pressure transmission, causing measurement errors.
Verify Range Settings: Confirm the transmitter's range settings are correct and match the actual measurement range. Improper range settings may result in out-of-range readings or reduced accuracy.
(3) Transmitter has no output:
Check power supply and circuitry: First verify the power supply is functioning normally. Then inspect the transmitter's circuitry for faults. Use tools like a multimeter to test components such as resistors, capacitors, and diodes for proper operation.
Check sensor connection: Verify the connection between the sensor and transmitter is secure, with no loose or disconnected parts. If the sensor connection is faulty, the transmitter cannot receive pressure signals, resulting in no output.