Modicon - Read RTD temperaturs less than zero

[Trevlar]

We have a Modicon Quantum with an ARI 030 10 RTD card installed. We are adding a PT100 3-Wire RTD to the card. The range that we need to display is -50 to 150 deg.C. We select the correct RTD type in Traffic Cop. Using a decade box, we can read the correct temps until we get below 0 C. Then the register shows overflow. (<9999). What must we do to get the register to display minus temp values? We cannot find anything about this in the Quantum Hardware or Logic Block Library guides. Thanks!

 

[Mickey]

I'm not a Modicon user but Google turned this up. See link below.
Note the reply, does it mean anything to you?

http://control.com/thread/1026218840

 

[Trevlar]

I'm not a Modicon user but Google turned this up. See link below.
Note the reply, does it mean anything to you?

http://control.com/thread/1026218840

I did see that note from Google also. Not sure what the response was for as ProWorx NxT (programming software) does not have the 'online>RDE online' option or the UINT data types available in the card config. Thanks for trying!

 

[theDave2]

My solution (abet ugly) would be to put a resistor (25 ohms)in series with the rtd and then rescale the value in the plc.

 

[shooter]

in modsoft check the the input range and the input data format it should be 16 bit signed and not 16 bit unsigned.

 

[mrjoseph]

-50= zero in the plc
150= 4095 in the plc

 

[Bitmore]

Just sounds like a problem in your comms setup and data storage, or perhaps one of the pesky larger or smaller numbers expressed in scientific notation.
Or perhaps Injun byte reverse problems.

Just a bitmore....

 

[Trevlar]

-50= zero in the plc
150= 4095 in the plc

Close. This RTD card (ARI03010) does not give 0-4095, it gives the raw temp value (in either F or C, user configurable). So, when we set it up for C, and have at +50, it reads +50, the problem is crossing below a zero value (or close to it). The cut-off appears to be -17.7 C. What we have done for now, is masked out the 16th bit, making the negative value a positive one and applying a -0.1 scaling factor at the HMI level. This will work for us now, but I don't understand why it won't allow the RTD card to drive the negative value lower than -17.7 without overflowing... Thanks for all of the advice.

 

[mrjoseph]

on the offline you can choose the rtd type that will allow you to go a negative number