Electrical Guy needs help

Hi,

We have the temperature tanks which are controlled by the s7-300 PLC.PT 100 with a range of -10 to 90 are connected to the temperature transmitter(-10 to 90) which sends a signal of 4-20mA to the PLC to control the solenoid valve which allows the flow of glycor to pass and chill the tank depending on the setpoint at the scada(15degrees).The problem we have is that the temperature in the tank is not corresponding with the one at the SCADA.is it possible to caliberate the temperature transmitter?if yes how do you do that?

1. Check if the 4-20mA signal is correct.
2. If 4-20mS signal is OK, then find the scaling function in the PLC and check if it is programmed correctly. It is quite likely that the library block FC105 "SCALE" has been used.

chama mulenga said:

is it possible to caliberate the temperature transmitter?if yes how do you do that?

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It all depends on the type of temperature transmitter used. Some can be calibrated, come can't. We don't have enough info to help you any further, unless you provide us the type and make of the transmitter.

Maybe the calibration can be done in the S7-300 analog card, but then we need the type of card used, which is also info you didn't provide.

And if both are impossible, then the last resort is to calibrate in the PLC software. But maybe the program has to be altered to make that possible.

Kind regards,

First: "PT 100 with a range of -10 to 90" ?? PT100 don´t have this range, only the converter is adjusted for this range. To see if the PLC and Scada have the scale ok, just replace the transmitter by a 4-20mA simulator. If the simulator is sending 4mA, you should read -10ºC in the scada. If the simulator is sending 20mA, you should read 90ºC in the scada. If this is OK, then your problem is in the PT 100 or transmitter. If you have a PT100 simulator, you can see if the transmitter is OK.
Note: 15ºC should give you 8mA.

I think he means that the integrated 4-20mA transmitter is calibrated to -10 .. +90 degrees.
That is why he should check as the 1st step if the mA signal really follows the actual temperature. That tells him if the problem is in the sensor, or in the program.
edit: I see that nonuke has answered it more detailed already.

calibrate a sensor:
take the sensor to the workshop and find a power supply and mAmeter.
connect it all together.
Now find some ice and adjust zero to be 0-(-10)= 10 10/100*16+4 = 5.6 mA
put sensor in hot water (with a thermometer in it)
example is 50 Celsius being 60/100*16+4 = 13.6 mA adjust scale.
if this correct check scaling in PLC.
check what goes in with mA meter and calculate what you should read.

Hi,
Thankyou very much for your ideas and l have leant something. Basically what we did was we replaced the temperature transmitter afer simulating 4-20mA signal to the A/I card and it worked.