Dear all!

I maintain a SNAP PAC system, and I get from some SNAP-AIRTD module IVAL and XVAL value: “-1.#QNAN”.
This values periodically change from the normal field value and back to “-1.#QNAN”. It happens almost every second.
The field specialist didn’t find any problem in the loops and in the power supply of the rack. He tried to restart the rack, but the problem didn’t solve.
I attached a picture of the IO Unit. The problem is on the module 8 to 12.

Many thanks for any idea.

Sincerelly, Peter


Hi Peter,

Be sure and email support @ and get those guys on the job.

My gut tells me, even though you have checked it, we are looking at a power supply issue…
You measured 5.1 volts between the green terminal and the end of D2 (the diode nearest the capacitor)?

Also have you measured the RTD disconnected from the module? Pull the connector out the top and see if the problem persists.
Don’t forget to measure for DC and AC (as well as resistance) on the probe in case there is a crossed wire or some amount of noise getting into the system.

Those are my quick thoughts on the matter.


Its a little late now, but I experienced this exact same issue. Turned out to be a bad brain (EB1-FM). It appeared to be constantly ressetting. It was a new brain, maybe 6 months old but never used and fresh out of the box. Firmware update did not help it either. But a different brain did : )