How to solve the common problems of pressure transmitters, we Kunco Instruments came out to refute the rumors

  Recently, because the title of "Ice Cream Assassin" has continued to occupy the top spot in the hot search list, Zhong Xuegao's ice cream has also been questioned. From the beginning of the Snow Lotus incident, it was just fermented by netizens. The praise and support continued, and now Zhong Xuegao has caused controversy, and the official person in charge also immediately issued a document to refute the rumor, explaining the importance of the incident and solving the problem. For this series of operations, the editor thought about how we should solve the problem and solve the confusion when we often use it in our chemical flowmeters. Our Weihai Kunke flowmeter came out to refute the rumor.

  The use of pressure transmitters in flow measurement is an instrument that we often apply. In the process of use, how to deal with and solve common faults of pressure transmitters, we will remove the reasons from the following points:

  1. The transmitter has no output

  1: Check whether the power supply of the transmitter is reversed; solution: connect the polarity of the power supply correctly;

  2: Measure whether the power supply of the transmitter has 24V DC voltage; Solution: It must be ensured that the power supply voltage supplied to the transmitter is greater than or equal to 12V (that is, the voltage at the input terminal of the transmitter power supply is greater than or equal to 12V). If there is no power supply, check whether the circuit is disconnected and whether the detection instrument is selected incorrectly (input impedance should be ≤250Ω);

  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 the short circuit, it means that the meter head is damaged); Solution: If the meter head is damaged, it needs to be replaced header.

  4: Connect the ammeter in series with the 24V power supply loop to check whether the current is normal; Solution: If it is normal, the transmitter is normal. At this time, check whether other instruments in the loop are normal. 5: Whether the power supply is connected to the power input end of the transmitter; Solution: Connect the power cord to the power supply terminal.

  2. Transmitter output ≥ 20mA

  1: Whether the power supply of the transmitter is normal; solution: if it is less than 12VDC, check whether there is a large load in the loop, and the input impedance of the transmitter load should meet RL≤(transmitter supply voltage -12V)/( 0.02 A) Ω;

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

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

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

  5: Is the power cord wiring correct? Solution: The power cord should be connected to the corresponding terminal;

  3. Transmitter output≤4mAOutput≤4mA

  1: Whether the transmitter power supply is normal Solution: If it is less than 12VDC, check whether there is a large load in the loop, and the input impedance of the transmitter load should meet RL≤(transmitter power supply voltage -12V)/( 0.02A ) Ω;

  2: Whether the actual pressure exceeds the selected range of the pressure transmitter; Solution: Re-select a pressure transmitter with an appropriate range. Whether the pressure sensor is damaged, severe overload sometimes damages the isolation diaphragm. Solution: It needs to be sent back to the manufacturer for repair.

  4. Incorrect pressure indication

  1: Whether the transmitter power supply is normal Solution: If it is less than 12VDC, check whether there is a large load in the loop, and the input impedance of the transmitter load should meet RL≤(transmitter power supply voltage -12V)/( 0.02A ) Ω;

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

  3: Whether the range of the pressure indicating instrument is consistent with the range of the pressure transmitter Solution: The range of the pressure indicating instrument must be consistent with the range of the pressure transmitter;

  4: Whether the input of the pressure indicating instrument and the corresponding wiring are correct Solution: If the input of the pressure indicating instrument is 4~20mA, the output signal of the transmitter can be directly connected; if the input of the pressure indicating instrument is 1~5V, then A resistor with an accuracy of 1/1000 or more and a resistance value of 250Ω must be connected to the input end of the pressure indicating instrument, and then connected to the input of the transmitter.

  5: The input impedance of the transmitter load should comply with RL≤(transmitter supply voltage -12V)/( 0.02A) Ω Solution: If it does not comply, corresponding measures can be taken according to the difference: such as increasing the supply voltage (but must be lower than 36VDC), reduce the load, etc.

  6: Check whether the input terminal of the multi-point paper recorder is open when there is no record; Solution: If it is open, then: a. No other loads can be carried; b. Use other recorders with input impedance ≤ 250Ω when there is no record.

  7: Whether the corresponding equipment shell is grounded Solution: The equipment shell is grounded;

  8: Is it separate from the AC power supply and other power supplies? Solution: Separate the wiring from the AC power supply and other power supplies;

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

  10: Whether there are sand, impurities, etc. in the pipeline that block the pipeline, and the measurement accuracy will be affected when there are impurities; Solution: Clean the impurities and add a filter before the pressure interface.

  11: Whether the temperature of the pipeline is too high, the operating temperature of the pressure sensor is -25~85℃, but it is within -20~70℃ in actual use. Solution: add a buffer tube to dissipate heat, add some cold water to the buffer tube before use, to prevent the superheated steam from directly impacting the sensor, thereby damaging the sensor or reducing the service life.

  Common faults are:

  1. When the pressure goes up, the pressure transmitter can’t go up: in this case, first check whether the pressure interface is leaking or blocked. If it is confirmed that it is not, check the wiring method, if the wiring is correct, then check the power supply, if the power supply is normal Then check whether there is output at the zero position of the sensor, or simply pressurize to see if the output changes. If there is a change, the sensor is not damaged. If there is no change, the sensor is damaged. Other reasons for this could be a broken meter, or a problem with other parts of the overall system.

  2. The output of the pressure transmitter does not change, but the output of the pressure transmitter changes suddenly, and the zero position of the pressure relief transmitter cannot return. The reason for this phenomenon is most likely caused by the sealing ring of the pressure sensor, which has been encountered several times in the use of our customers. Usually due to the specification of the sealing ring (too soft or too thick), when the sensor is tightened, the sealing ring is compressed into the pressure-inducing port of the sensor to block the sensor. When the pressure is pressed, the pressure medium cannot enter, but when the pressure is too large, it suddenly bursts open. The sealing ring and the pressure sensor are changed by the pressure, and when the pressure is reduced again, the sealing ring returns to block the pressure inlet, and the remaining pressure cannot be released, so the zero position of the sensor cannot go down. The way to eliminate this reason is to remove the sensor and directly check whether the zero position is normal. If it is normal, replace the sealing ring and try again.

  3. The output signal of the transmitter is unstable. The reasons for the unstable signal are as follows:

  (1) The pressure source itself is an unstable pressure;

  (2) The anti-interference ability of the instrument or pressure sensor is not strong;

  (3) The sensor wiring is not strong;

  (4) The sensor itself vibrates very strongly;

  (5), sensor failure;

  4. There is no output when the transmitter is connected to electricity. The possible reasons for the pressure transmitter are:

  (1)connect the wrong wire (check both the instrument and the sensor);

  (2) Open circuit or short circuit of the wire itself;

  (3) The power supply has no output or the power supply does not match;

  (4) The instrument is damaged or the instrument does not match;

  (5) The sensor is damaged;

  5. The deviation between the transmitter and the pointer pressure gauge is large. First, the deviation is a normal phenomenon. Second, confirm the normal deviation range. The method of confirming the normal error range: Calculate the error value of the pressure gauge. For example: the pressure gauge range is 30bar, The accuracy is 1.5%, and the small scale is 0.2bar. The normal error is: 30bar*1.5%+0.2*0.5 (visual error)=0.55 bar;

  6. The error value of the pressure transmitter. For example: the pressure sensor range is 20bar, the accuracy is 0.5%, the instrument accuracy is 0.2%, and the normal error is: 20bar*0.5%+20bar*0.2%=0.18bar The possible error range of the overall comparison should be based on the equipment with large error value The error range shall prevail. For the above example, the deviation between the sensor and the transmitter can be regarded as normal within 0.55bar. If the deviation is very large, a high-precision instrument (at least this instrument is higher than the pressure gauge and sensor) should be used for reference.

  7. The influence of the installation position of the differential pressure transmitter on the zero output: Because the differential pressure transmitter has a small measurement range, the self-weight of the sensing element in the transmitter will affect the differential pressure transmitter. output, so the zero position change that occurs when the differential pressure transmitter is installed is normal. During installation, the axis of the pressure sensitive part of the transmitter should be perpendicular to the direction of gravity. If the installation conditions are limited, the zero position of the transmitter should be adjusted to the standard value after installation and fixation.