Why do I get "comm err:2" on 4-20mA input channels bouncing around 4mA?

[GK_Associates]

I am using the new dual channel FP-AI-C420 analog input modules and whenever the input signal is at zero (4mA), the module causes a comm error 2 alarm in Lookout. If you monitor the channels in the Field Point software you can see the channels in questions switching from "Success" to "Out of Range" as the signal drops below 4mA. This is filling up the alarm files in the Lookout database very rapidly (over 100,000 in three days!).

How do I resolve this problem?

Thanks in advance,
Geoff Klotz
GK Associates, Inc.

[Aaron_G]

Geoff,

FieldPoint modules return status as a 2 bit number (4 states; good, unconfigured, channel specific error 1, channel specific error 2). The FP-AI-C420 module reporting Channel Specific Error 2 means that the input signal is out of range (less than 4 mA or greater than 20 mA). One option is to make sure your signal does not go out of range. Note: whereas FieldPoint I/O modules provide over-ranging (e.g. 3.5 mA to 24 mA on the FP-AI-100), the FieldPoint Dual Channel Modules do not have over-ranging.

If you have version 4.0.1.55 or later of the fpoint.cbx and Lookout, you may be able to filter the alarms. To filter the alarms, create a fpoint.ini file in the lookout directory and add the following lines to filter channel specific alarms:

[FieldPointTagName]
Filte
rChAlarms=1

A value of 0 for FilterChAlarms will allow all alarms, whereas a value of 1, filters Channel Specific Error 1. I do not know at the moment whether a value of 1 will also filter Specific Error 2, or if a value of 2 will filter specific error 2. It may be that there is not an option for filtering Specific Error 2 at this point in time. I have to double check on this and will add the information when I can.

Regards,
Aaron

[GK_Associates]

Aaron:

Thanks for your reply. I actually thought about replacing the three dual-channel AI modules with a FP-AI-110 module to fix this (an I may still have to do this), but I thought there was something simple I could do to prevent Lookout from logging these alarms. I already set a filter inside Lookout to ignore all "comm" alarms, but this simply disables the alarms to the screen. They are still filling up the drive with unwanted data in the Citadel database. This also serves to disable the "comm lost" notification to the operator which we rely upon for serial communication problems.

I will try playing around with your idea to filter the alarms in the fpoint.ini file.
It seems ridiculous that is no way to turn off the logging of a particular a
larm to Citadel. It seems more ludicrous that these dual-channel AI modules have no provision for overranging. I also sent this original request to NI support and will wait to see what they have to say about it.

Regards,
Geoff

[Aaron_G]

Geoff,

The fpoint.ini entry does prevent the "channel specific" alarms from being logged (they are not "Comm" alarms). However, the filter modification was only done for specific error 1, not specific error 2, so it will not help. I will be seing if we can modify the driver to also allow filtering of specific error 2. What version of Lookout do you have?

Aaron
National Instruments
FieldPoint R&D

[GK_Associates]

Aaron:

We are currently using Lookout 4.5 build 9.