IO Bod for Rockwell Point IO

[TommyKnudsen]

Hi

I´m using Rockwell Controllogix and Point IO. Regarding analogue input card and RTD - how can I configure the raw count to go to zero with bad IO ? I can't find that options.

/ Tommy

 

[Ken Roach]

If zero is part of the valid range for the data value, you can't easily tell the difference between a valid zero and a fault indication.

That's why most modern analog input modules don't use an input value of zero to indicate a problem with the input signal, but rather force the input value to an out-of-range value as well as setting a separate fault indication bit.

The 1734 Temperature Module user manual (Publication 1734-UM004) says this about broken-wire detection:

The module has the ability to check for a broken or detached wire. In any mode, if a broken/detached lead is detected, the data value is forced to maximum and the overrange alarm is set. Once the alarm is issued, it remains active as long as the input signal is faulted.

I haven't tested this with the 1734-IR2 module, but I recently built a machine with 1734-IT2I modules using Type J thermocouples. The temperature input range in degrees F for that module is -346 to 2192, so when there is a broken wire the input value is forced to "21920" (the units are 1/10 of a degree).

The input ranges are in the Installation Instrutions booklet; 1734-IN011.

The 1734-IR2 with (for example) a 100 ohm platinum RTD has in input date range from -328 to 1598 degrees F, so I would expect the value to be forced to 15980.

 

[the_msp]

Hello, I have a 1734-IR2 with a 100 Ohm RTD connected to it. I loosened the white wire and the value on my HMI went from 21.1 to 870.0 deg. The module config is set to 100 ohm PT 385, celcius, low eng 1000 high eng 5000. Went to 8700 with wire disconnected. And of course the LED for input 0 went from green to red.

 

[Ken Roach]

That makes sense; the range in Celsius for a 100 ohm PT RTD is -200 to 870 degrees C.

You should find also that the .Ch0Overrange bit is true when the wire is broken, no matter what units are selected for the module temperature data.

 

[TommyKnudsen]

Thanks for the input - I´m just wondering if it was possible to configure the raw count to go to zero .... or minimum value when I have a broken wire, but it don't seems to be possible.

 

[Ken Roach]

It is not possible to configure the module to send the controller a value of zero when there is a broken wire to the RTD sensor.

This is a purposeful feature of the module, because "0.0 degrees F" or "0.0 degrees C" is a valid temperature for the module to sense.

You can certainly copy or scale the module data and represent it as zero to an HMI in the event of a broken-wire detection and high-limit value.