MC4xFS: VIN combined with CIN as safety function

Sorry, I was asking for MC4x, not MD4

Hi Frank,

Since you are posting this question, I am guessing you received the MC4xFS instruction book from your local Parker reps. the other week? 

In general it is a good idea to add a second input channel that is reading a separate sensor, as this makes it possible to handle random sensor hardware faults that cause an erroneous signal that falls within the normal operating range.
One example of an in-range failure that is more of a systematic fault than a random sensor fault is loss of ground. 

Loss of ground will on some sensors lead to an erroneous signal that that is not detected by a range check, the value that is read can depend on the input characteristics. 

It sounds as if the connection you are suggesting is to use a single output signal sensor, with the CIN as the sensor ground connection instead of -VREF ?
I am not sure if that connection will work or if it in itself could cause problems due to the measurement resistor, but if it does work then it might possibly be used to detect loss of ground. 
Such an installation would still not help with random sensor in-range faults, so a design that is doubling up with a redundant and diverse sensor is better. 

One more thing, Specifically for the MC4xFS; 

If the second channel is reading a crossed sensor signal (for example two VIN:s reading IQAN-LST VOUT-A and VOUT-B), or if the second channel is dot dependent on A/D conversion (e.g. one VIN and one PWMIN), then the safety function could be designed with tighter tolerances.  

For those reading this and not recognizing the reference to information about safety functions in the MC4x instructions; this is from the MC4x instruction book update for the MC4xFS modules, check with your local Parker rep to get the information needed to start designing with MC4xFS already now. When MC4xFS is officially launched (next month) the safety manual will be publicized on parker.com.