Guys, looking for some help at a customer site...
I need to add open wire detention to a system using 1794-IE8 and 1734-IE4C modules.
For the 1794-IE8, it's configured as 4-20mA mode. (Under-range does not apply to 0-20mA mode).
Originally, I thought piece-o-cake. Just look at the under-range bits and trigger errors off of that. Well, shame on me for thinking life can be so easy. Turns out that the under-range bit is triggered when the signal is AT or below 4mA. Well, I have a few pressure transmitters which are loop powered. 4mA = 0 PSI, and at an "IDLE" state the transmitter is putting out 4mA and the under-range bit is being set. This is clearly not a broken wire situation, therefore I cannot use this as a broken wire trigger.
I have not looked too deep into the 1734-IE4C cards yet, but I assume a similar situation may occur.
Open to suggestions on how to detect an open wire w/o false triggers, basically trying to reliably detect if I have a bad 4-20mA analog transmitter.
I need to add open wire detention to a system using 1794-IE8 and 1734-IE4C modules.
For the 1794-IE8, it's configured as 4-20mA mode. (Under-range does not apply to 0-20mA mode).
Originally, I thought piece-o-cake. Just look at the under-range bits and trigger errors off of that. Well, shame on me for thinking life can be so easy. Turns out that the under-range bit is triggered when the signal is AT or below 4mA. Well, I have a few pressure transmitters which are loop powered. 4mA = 0 PSI, and at an "IDLE" state the transmitter is putting out 4mA and the under-range bit is being set. This is clearly not a broken wire situation, therefore I cannot use this as a broken wire trigger.
I have not looked too deep into the 1734-IE4C cards yet, but I assume a similar situation may occur.
Open to suggestions on how to detect an open wire w/o false triggers, basically trying to reliably detect if I have a bad 4-20mA analog transmitter.