Mike Sensing | General failures and solutions of 4~20mA transmitters

Initial inspection and testing

Solution

Check whether the power supply is reversed

Connect the power polarity correctly.

Measure the power supply of the transmitter, whether there is 24V DC voltage

It must be ensured that the power supply voltage to the transmitter is ≥12V (intelligent type) ≥15V (common type). If there is no voltage, check whether the circuit is open, check the secondary instrument/PLC sampling resistance (input impedance should be ≤250Ω)

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 the meter head is damaged)

Replace the meter head

Connect the ammeter into the 24V power supply loop to check whether the current is normal

If it is normal, the transmitter is normal. At this time, check whether other instruments in the loop are normal.

Whether the wiring is loose

Connect the wires and tighten them.

Whether the power supply is correctly connected to the transmitter power input terminal

Correctly connect to the power terminal according to the power requirements

Initial inspection and testing

Solution

Whether the transmitter power supply is normal

If it is less than 12VDC, check whether there is a large load in the loop. The input impedance of the transmitter load should conform to RL≤(transmitter supply voltage-12V)/(0.02A) Ω

Whether the actual pressure exceeds the upper limit of full scale

Reselect a pressure transmitter with appropriate range

Whether the sensor is damaged, severe overload can sometimes damage the isolation diaphragm

Need to be returned to the factory for overhaul

Whether the power cord wiring is correct

The power cord should be connected to the corresponding terminal

Initial inspection and testing

Solution

Whether the transmitter power supply is normal

If it is less than 12VDC, check whether there is a large load in the loop. The load capacity of the transmitter should conform to RL≤(transmitter supply voltage-12V)/(0.02A) Ω

Whether the wiring is loose and the contact resistance increases, which is equivalent to an increase in the load

Connect the wire and tighten it, the load conforms to RL≤(transmitter supply voltage -12V)/

(0.02A) Ω

Whether the actual pressure exceeds the selected range of the pressure transmitter

Reselect a pressure transmitter with appropriate range

Whether the sensor is damaged, severe overload can sometimes damage the isolation diaphragm

Need to be returned to the factory for overhaul

Initial inspection and testing

Solution

Whether the transmitter power supply is normal

If it is less than 12VDC, check whether there is a large load in the loop. The load capacity of the transmitter should conform to RL≤(transmitter supply voltage-12V)/(0.02A) Ω

Whether the reference pressure value must be correct

Replace the products of the same model. If the error is the same, refer to the pressure instrument for testing. If the instrument accuracy is low, you need to replace it with a higher accuracy instrument.

Whether the range of the secondary instrument is consistent with the range of the pressure transmitter

Adjust the range of the secondary instrument must be consistent with the range of the pressure transmitter

The load capacity of the transmitter should meet RL≤(transmitter supply voltage -12V)/

(0.02A) Ω

If it does not meet the requirements, corresponding measures can be taken according to its differences: such as increasing the supply voltage (but must be lower than 36VDC), reducing the load, etc.

Whether the corresponding equipment shell is reliably grounded

Reliable grounding of equipment shell

Whether the strong current and weak current are wired separately on site

Scientific and reasonable wiring to avoid instability/error of transmitter signal caused by interference

The sensor diaphragm is easy to deform, overload, foreign objects, hard objects sometimes damage the isolation diaphragm

Need to be returned to the factory for overhaul

Impurities in the pipeline will affect the measurement accuracy

Impurities need to be cleaned up, and a filter screen is added before the pressure port