When the analog current input read is inside a limited range of values, the TM3AI8  module provides to the PLC the analog read value inside some  PLC object %IWx.i  together with the diagnostic information  “no error”  or “normal”, that means the PLC application can use it normally (without restriction).

When the input read value is outside the limited range of value , the diagnostic information becomes as “ value out of range”  , then the PLC application have to care about the diagnostic , but not to the provided value %IWi.x (which is no more the real one seen by the TM3 module,  but a truncated value equal to the limit value)

The below table gives the limit range values which involve the channel diagnostic being as “limit exceed” (value 5 for low limit and  6 for high limit), according the different configuration modes available for current measurement within the TM3AI8 module

Configuration mode	Low limit value	High limit value
0-20mAmp	-0.4 mAmp	20.4 mAmp
4-20mAmp	3.68 mAmp	20.32 mAmp
0-20mAmp Extended	-0.4 mAmp	23.54 mAmp
4-20mAmp Extended	1.20 mAmp	23.17 mAmp

We can see the limit is always different , whatever is the selected mode

Note: for other analog input modules managing current mode: TM3AI2, TM3AI4, TM3AM6 , TM3TI4, TM3TM3, they  have same limit values ,as shown into the table above, for 0-20mAmp and 4-20mAmp and they do not support the two “extended” modes.

Released for:Schneider Electric New Zealand