AB Relay Output Issue

jimwawar47

Member
J
Join Date
Dec 2010
Location
Halifax
Posts
21
This one has me stumped.


I have a 1756-L61 controller communicating over device net. One of the chassis has a 1764-OW8/A output relay card. Channel one goes high and stays high. If the system is reset the channel one goes low. As soon as the channel goes high, it stays high.



The light to indicate the output as being high is off, but power is passed.

Looking at the value in RSLogix5000 the output is shown as being off, but power is passed.
The card and the back plane have both been replaced.

With the card removed the back plane was checked and did not pass power.

The new card was swapped with another card for sanity, power was still passed on channel one. The new card placed in the other chassis did not pass power on channel one.



I have a support request into AB also.
 
What do you mean power is being passed? I believe those outputs have a snubber resistor or whatever and if you take a reading with a standard multimeter you will see leakage voltage. Try using a Wiggy or put a real load across it like a light bulb.
 
By power being passed, I mean the device being activated by the channel is turned on. I wouldn't expect this from a voltage leak.
 
jimwawar47 said:
By power being passed, I mean the device being activated by the channel is turned on. I wouldn't expect this from a voltage leak.
Click to expand...

Depends on the device. Resistive or inductive. Resistive/electronics can be turned on.

Once turned on the leakage can be enough to keep it on.
 
Last edited:
several things come to mind.
1. the output is bas, but you replaced the card and the issue still exists.
2. the output is in a latched on start in the program.
3. just a guess, the output is programmed to remain in the last state when the power is lost, the mcr opens and the power is killed. when the power is restored, the mcr energizes and the output power is restored since the output is in a latched on state.
4. bubba modified the program. has any changes been made recently? I would check the program against the backup files.
hope this helps,
james
 
Last edited:
I am wondering what card this is. I am not familair with "1764-OW8". Perhaps this is a 1794-OW8 and it is connected using a 1794-ADN over DeviceNet. That is my assumption.

The LED indicator should match the device status, or at least what you measure at the output point. Whether Bubba changed the program or not. And, what you are describing says they do not match, at least when it should be OFF.

If your logic turns the ouput ON, does the module indicator turn ON? Then does it turn OFF when the logic turns the output OFF? I am just talking about the indicator, not the field device.

Also, on the 1794-ADN what is the status of the indicators on that module? Specifically the MOD/NET and I/O Status indicators. What is the status when the output is logically ON and logically OFF (if different).

OG
 
Does the Device Net scanner report any loss of device faults?
A possible scenario: Energizing the circuit controlled by the output creates a condition that drags down the power to the entire Device Net drop and it drops off the bus. The drop is configured to hold its last state upon loss of Device Net communications. You can test this by monitoring the other outputs on the same drop while the one you're concerned with is showing the abnormal behavior. If you still have full control of the other seven outputs on the module, then my hypothesis is disproved.
 
Operaghost said:
I am wondering what card this is. I am not familair with "1764-OW8". Perhaps this is a 1794-OW8 and it is connected using a 1794-ADN over DeviceNet. That is my assumption.
OG
Click to expand...


You are correct it is 1794-OW8 over DeviceNet.


Operaghost said:
The LED indicator should match the device status, or at least what you measure at the output point. Whether Bubba changed the program or not. And, what you are describing says they do not match, at least when it should be OFF.

If your logic turns the ouput ON, does the module indicator turn ON? Then does it turn OFF when the logic turns the output OFF? I am just talking about the indicator, not the field device.
OG
Click to expand...


Yes, when the output is on the indicator turns on, when the output is turned off the indicator turns off.


Operaghost said:
Also, on the 1794-ADN what is the status of the indicators on that module? Specifically the MOD/NET and I/O Status indicators. What is the status when the output is logically ON and logically OFF (if different).

OG
Click to expand...
I am off site right now, I'll check it on Monday when I return.
 
So the IO indicator shows correct for the logic?

But even in the off state current is flowing?

What kind of load is being driven? Does the load actually operate?
 

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