ControlLogix "trap" Power Down

[VulcPAC]

Hi:
For ControlLogix.
Is there a way to "trap" when processor is powering down? This mean leave a bit latched or a value written to a tag? Is there a flag or a fault code that can be used?
I need to capture a value of counts from an absolute encoder in a DINT tag (encoder in a Powerflex that loose position when is power down), so when processor is power-up again, I can write that tag as a reference with the first scan bit.

Regards

 

[TheRooster]

I wonder if you can use an event task that triggers when the processor first loses power but still is on. Like maybe a minor controller fault or when it starts using the battery for a couple seconds before fully shutting down, I'm not sure what it would be but that's what I would try.

 

[James Mcquade]

write the encoder value to a register every scan, if it's a long scan time, create a new routine with a 2ms execution time (or other time).
when the plc powers down, you have the last encoder position. it will be close, but not exact if the encoder has a lot of inerita. when the plc powers back up,
use the first scan bit to move the register info to a location.

the only downside to this - when the plc is powered down, what if maintenance moves the shaft the encoder is connected to?
just my thoughts.
james

 

[VulcPAC]

write the encoder value to a register every scan, if it's a long scan time, create a new routine with a 2ms execution time (or other time).
when the plc powers down, you have the last encoder position. it will be close, but not exact if the encoder has a lot of inerita. when the plc powers back up,
use the first scan bit to move the register info to a location.

the only downside to this - when the plc is powered down, what if maintenance moves the shaft the encoder is connected to?
just my thoughts.
james

Thanks for your answer.
Fortunately this machine de-energizes when the motor is stopped so there are no inertia problems. In case this happens, when turning on the machine you must manually jog to a Home position and set the value there. The register that I need to retain is when they have stopped the encoder in a no home position. I'm going to try the 2 ms solution.

 

[joseph_e2]

...
I need to capture a value of counts from an absolute encoder in a DINT tag...

If it's an absolute encoder, why do you need to trap its value? Or is it really an incremental encoder that's homed after a power cycle?

 

[VulcPAC]

If it's an absolute encoder, why do you need to trap its value? Or is it really an incremental encoder that's homed after a power cycle?

Is an absolute encoder, but the routine in PLC that handle the logic is very "creepy" to modify, and it works with own values of position, offswt, home, final position, so it need to be referenced after a power up. Is not the encoder, is the auxiliary values that reference to that encoder.

Regards

 

[Chuck Woodbury]

Sounds like you need to rewrite the code and simplify it. Make it "Not Creepy". Good training project for up and coming programmers if you have some.