AB 1756-OF8I Open Wire Detection

[Diaa]

Hi Guys,

For Allen-Bradley 1756-OF8 module, the channel status word has a bit for open wire detection "ChxOpenWire". I checked for the 1756-OF8I module, it doesn't seem that it has a similar status bit.

Anyone can advise if the channel open wire can be reported for the "1756-OF8I" module? how?

Thanks

 

[Paullys50]

You'd have to look in the manual. Generally speaking you can achieve broken wire detection by looking at the raw data. Of course, the setup of the raw data for 4-20mA can vary pending the IO card (1756, 1769, 1734, 1794) so I always evaluate the raw data directly.

4mA I set so I get some value (never 0). I then set a % tolerance to calculate lower/upper limits for my raw data. Say I'm using a 1794-IE8 card. Setting the card to measure 0 - 20mA gives a raw count of 6240 @4mA. If I assume a 5% tolerance, any raw data below 5928 will issue a fault. I use this example because FlexIO counts aren't really configurable. Applying the same methods on other IO families provides consistent fault detection.

 

[Diaa]

You'd have to look in the manual. Generally speaking you can achieve broken wire detection by looking at the raw data. Of course, the setup of the raw data for 4-20mA can vary pending the IO card (1756, 1769, 1734, 1794) so I always evaluate the raw data directly.

4mA I set so I get some value (never 0). I then set a % tolerance to calculate lower/upper limits for my raw data. Say I'm using a 1794-IE8 card. Setting the card to measure 0 - 20mA gives a raw count of 6240 @4mA. If I assume a 5% tolerance, any raw data below 5928 will issue a fault. I use this example because FlexIO counts aren't really configurable. Applying the same methods on other IO families provides consistent fault detection.

Thanks a lot for your reply!

I checked the manual before asking here. but there's no mention for channel open detection for 1756-OF8I, however, the alarm is clearly mentioned in the 1756-OF8 manual under "Channel Status Word".

Speaking of raw data evaluation, This should be applicable for analog input channels, but I don't think you can do the same for the outputs, the module in discussion here is an analog output module.

Please let me know if I'm wrong? I'm fairly new to AB configuration.

Cheers

 

[Paullys50]

I rushed my post and made an assumption w/o looking at the specifics of your part number. Can't say I'm aware of broken wire detection on an Analog Output channel.