How to disable "Channel error" on a configured but unused input channel
I have a delicate question which probably is just as odd as it's tricky to solve :)
In a project I'm currently programming I'm using a AC800 PM851 with S800 I/O:s to collect and distribute a number of temperature measurements through a OPC server to a centralised display system.
Now to the question: I have to supply/configure (but unused) channels on my AI835 and AI845 I/O:s for future measurements that can easily connected by maintenance personel without any knowledge of the control system (the PM851) and it´s application. Hence they must be plug-and-play; connect a thermocouple to the MTU and the preconfigured channel will display a value on the display system and remove it when finished.
However, I can't find any way to disable the "Channel error" trigger on these unused (and pre-configured) channels, resulting in a sum alarm for that I/O further along in my program. Setting the 'Activate channel' to FALSE makes no difference; if the channel has a connected variable to it, it will result in a channel error if there no electrical connection. I really want to avoid putting thermocouple jumpers on the MTU for these channels just to get rid of the alarm.
It is OK as a last resort to entirely disable the warning-flag for the AI-unit(s) affected but here comes a even more tricky bit: on one of the AI845 I/O:s the two first channels are used permanently and the rest are these preconfigured, temporary channels. In that case it would be uncomfortably to risk having a failure (warning) on one of these channels to go unnoticed until the operator detects this himself on the the display panels that there's no value presented but there was no alarm at the point of failure.
Tricky ey? Any help or suggestions is very grateful :)
I remember an issue with warnings on AI835 for not used channels. But I think it was together with AC450 & AF100, anyhow the board probably report the same with AC800.
One problem with the warning indication on the AI835 boards depends on the cold junction compensation channel 8. If cold junction channel 8 is not used you have to set the CJC compensation parameter to 1=(No CJC, fixed compensation) on all channels to get rid of the warning. (also on not used channels).
I don't know which CJC option you use ?, fixed?, Channel 8? or one common channel from the system ( only possible with AC800M)
Another option (if you only have a few boards), is to jumper all not used channels so they became within a valid measuring range. I have seen that on some sites.