Common fault analysis and treatment methods of capacitive pressure transmitters

Inspection & Testing

1. Check whether the power supply of the transmitter is reversed;

2. Measure the power supply of the transmitter to see if there is a 24V DC voltage;

3. If it is with a meter head, check whether the meter head is damaged (you can short circuit the two wires of the meter head first, if it is normal after short circuit, it means that the meter head is damaged);

4. Serial the ammeter into the 24V power supply circuit to check whether the current is normal;

5. Whether the power supply is connected to the power input of the transmitter;

Solution

1. Connect the power supply polarity correctly.

2. The power supply voltage of the transmitter must be guaranteed to be 12V (that is, the voltage of the power input terminal of the transmitter is 12V).

3. If there is no power supply, check whether the circuit is disconnected and whether the detection instrument is selected incorrectly (the input impedance should be 250q);

4. If the meter head is damaged, it needs to be replaced, if it is normal, it means that the transmitter is normal, and other instruments in the circuit should be checked to see if it is normal.

5. Connect the power cord to the power terminal.

Common faults: the indication is too large - confirm whether the range and zero position are set and calibrated, whether there is condensate in the impulse pipe, and whether there is leakage in the negative pressure chamber and pipeline.

The indication is small - confirm whether the measuring range and zero position are set and calibrated, and whether there is any leakage in the positive pressure chamber and pipeline.

No indication - whether the power supply is wired correctly and whether the voltage is within the operating range.

The two pressures of the measured medium of the capacitive pressure transmitter pass through the high and low pressure chambers, act on the isolation diaphragm on both sides of the δ element (i.e., the sensitive element), and transmit to both sides of the measuring diaphragm through the separator and the filling liquid in the element. A capacitive pressure transmitter consists of a capacitor consisting of a measuring diaphragm and electrodes on both sides of the insulating sheet. When the pressure on both sides is inconsistent, the displacement of the measuring diaphragm is proportional to the pressure difference, so the capacitance on both sides is unequal, and it is converted into a signal proportional to the pressure through the oscillation and demodulation links.

Capacitive pressure transmitters and capacitive absolute pressure transmitters work on the same principle as differential pressure transmitters, except that the pressure in the low-pressure chamber is atmospheric or vacuum. The AD converter of a capacitive pressure transmitter converts the current from the demodulator into a digital signal, the value of which is used by the microprocessor to determine the input pressure value. The microprocessor controls the operation of the transmitter.

In addition, it performs sensor linearization. Reset the measurement range. Engineering unit conversion, damping, prescribing, sensor fine-tuning, and other calculations, as well as diagnostics and digital communication.

1. The transmitter does not return to zero when there is no pressure?

Answer: The elimination method is to remove the transmitter from the installation position, observe whether the zero position is normal, and if so, replace the pipe seal. At the same time, check whether the transmitter is installed perpendicular to the pipe, if not, the transmitter zero position can be adjusted.

2. No output?

Answer: Check whether the 24V power supply is normal, and check whether the meter wiring with display is broken.

3. The output is too large?

Answer: Check the impulse pipe for residual gas or liquid, and clean it if so. At the same time, check whether the actual pressure on site exceeds the transmitter range, and if it exceeds the transmitter of the appropriate range, the transmitter of the appropriate range is reselected.

1. The transmitter has no output.

1. Check whether the power supply of the transmitter is reversed; Solution: Connect the power supply polarity correctly.

2. Measure the power supply of the transmitter to see if there is a 24V DC voltage; Solution: The supply voltage supplied to the transmitter must be 12V (i.e. the voltage at the input end of the transmitter supply is 12V).

If there is no power supply, you should check whether the circuit is disconnected and whether the detection instrument is selected incorrectly (the input impedance should be 250); Wait a minute.

3. If it is with a meter head, check whether the meter head is damaged (you can short circuit the two wires of the meter head first, if it is normal after short circuit, it means that the meter head is damaged); Solution: If the meter head is damaged, you need to replace the meter head, 4: string the ammeter into the 24V power supply circuit to check whether the current is normal; Solution: If it is normal, it means that the transmitter is normal, and you should check whether the other instruments in the circuit are normal.

5. Whether the power supply is connected to the power input of the transmitter; Solution: Connect the power cord to the power terminal.

2. The output of the transmitter is 20mA

1: Whether the power supply of the transmitter is normal Solution: If it is less than 12VDC, you should check whether there is a large load in the loop, and the input impedance of the transmitter load should be in line with RL (transmitter supply voltage -12V) (

2: Whether the actual pressure exceeds the selected range of the pressure transmitter; Solution: Re-select the pressure transmitter with the appropriate range.

3: Whether the pressure sensor is damaged, severe overload can sometimes damage the isolation diaphragm. Solution: It needs to be sent back to the manufacturer for repair.

4: Whether the wiring is loose; Solution: Connect the wire and tighten it.

5: Whether the power cord is wired correctly Solution: The power cord should be connected to the corresponding binding post.

3. The output of the transmitter is 4maoutput 4mA

1: Whether the power supply of the transmitter is normal Solution: If it is less than 12VDC, you should check whether there is a large load in the loop, and the input impedance of the transmitter load should be in line with RL (transmitter supply voltage -12V) (

2: Whether the actual pressure exceeds the selected range of the pressure transmitter; Solution: Re-select the appropriate range pressure transmitter Whether the pressure sensor is damaged, severe overload can sometimes damage the diaphragm.

Solution: It needs to be sent back to the manufacturer for repair.

4. Wrong indication

1: Whether the power supply of the transmitter is normal Solution: If it is less than 12VDC, you should check whether there is a large load in the loop, and the input impedance of the transmitter load should be in line with RL (transmitter supply voltage -12V) (

2: Whether the reference pressure value must be correctSolution: If the accuracy of the reference pressure gauge is low, it is necessary to replace the pressure gauge with higher accuracy.

3: Whether the range of the pressure indicator instrument is consistent with the range of the pressure transmitter Solution: The range of the pressure indicator instrument must be the same as that of the pressure transmitter.

How to deal with the problem of intelligent pressure transmitter:

1. What kind of connection is used between the pressure transmitter and other electronic equipment? Do you need a short-range connection? If you have a long-distance connection, do you need to use a connector?

2. The pressure transmitter needs to maintain stability after overtime work: most of the transmitters will produce "drift" after overtime work, so it is necessary to understand the stability of the transmitter before purchasing, and this kind of pre-work can reduce all kinds of troubles that will occur in future use.

3. Encapsulation of pressure transmitter. The transmitter's package, in particular, is often overlooked by its frame, but this will gradually reveal its shortcomings in later use. When purchasing a transmitter, we must consider the working environment of the transmitter in the future, what the humidity is, how to install the transmitter, whether there will be strong impact or vibration, etc.

4. Whether there is a need for an interchangeable transmitter. Determine if the required pressure transmitter can be adapted to multiple usage systems. In general, this is important.

Especially for OEM products. Once the product is in the hands of the customer, the cost of calibration is considerable. If the products are interchangeable, even changing the transmitter used will not affect the effectiveness of the entire system.

5. What kind of excitation voltage to choose. The type of output signal determines what kind of excitation voltage is chosen. Many amplification transmitters have built-in voltage regulation, so they have a wide range of supply voltages.

Some transmitters are quantitatively configured and require a stable operating voltage, so the available working voltage determines whether to use a sensor with a regulator, and the working voltage and system cost should be considered when selecting the transmitter.

The pressure transmitter microprocessor has 16 bytes of program RAM in it and three 16-bit counters, one of which performs a D conversion.

The da converter fine-tunes the data from the microprocessor and corrected digital signals, which can be modified with the transmitter software. The data is stored in EEPROM and is stored even if the power is off.

The digital communication line provides a connection interface for the transmitter to external devices such as the Type 205 Smart Communicator or a control system using the HART protocol. This line detects digital signals superimposed on 4-20mA signals and transmits the required information through the loop. The type of communication is frequency-shift keying, FSK technology and is based on the Beii 202 standard.

Analog features.

High precision. The measuring range and zero point are continuously adjustable externally.

Good stability and performance.

Positive migration can reach 500%, negative migration can reach 600% Second-line system.

Adjustable damping and overpressure resistant.

Solids sensor design.

There are no mechanical moving parts and the amount of maintenance is low.

Light weight ( The whole series has a unified structure and strong interchangeability.

Miniaturization (166 mm overall height).

Diaphragm materials for contact media are optional.

Unilateral overpressure resistance.

Low-pressure cast aluminum alloy housing.

Smart Features:

Superior measurement performance for pressure, differential pressure, level, flow measurement Digital Accuracy: +(

Analog accuracy: +(

Full Performance: +(

Stability: 60 months.

Turndown ratio: 100:1

Measurement rate: Miniaturized (all stainless steel flange, easy to install.)

The process connection is compatible with other products for optimal measurements.

The world's only sensor with an H-alloy sheath (patented technology) achieves excellent thermal and cold stability.

Smart transmitter with 16-bit computer.

Standard 4-20mA with HART-based digital signals, remote control Upgrades to fieldbus and field-based technologies are supported.