1794-VHSC Encoder reading 0

[ceilingwalker]

Hello all. I have an issue I have not been able to find an answer to online. I have a 1794-VHSC connected to a Contrologix PLC and a Sick incremental encoder. Everything works fine. I have a homing routine for setting a location of a device. I jog this device and have it scaled so that it is reading distance traveled. The issue I have is, for apparently no reason and at random times, the counter will read "0" as its position, requiring I run another homing sequence. I have tried a lot of different things to get it to intentionally write a "0" however, I can't do it. My preset is set and, as part of the homing sequence, it writes this value into the counter, after the home LS is made, then broke. Any ideas would be awesome. Thank you.

 

[Ken Roach]

The first two suspects are a power cycle and an unintentional trigger of a Reset input.

Have you intentionally tested both of those ?

 

[James Mcquade]

I had a similar issue years ago with a slc500.

I reseated all the cards and power supply to the rack several times to clean the terminal connection.

hope this helps,
james

 

[ceilingwalker]

The first two suspects are a power cycle and an unintentional trigger of a Reset input.

Have you intentionally tested both of those ?

No Sir, not yet. I am not very familiar with the encoder modules. I will test that today. Thank you.

 

[rdrast]

It is changing to zero randomly while powered up doing nothing?


I haven't seen that, but I never use the actual counter presets or controls for anything anymore after too many headaches.
Generally, I use a PMUL instruction with a small word size to generate a delta every scan, and add that into a separate register from the actual counter.
Also, by inhibiting the ADD instruction when the system is powering up, or in other instances I might desire, stray pulses and such are ignored.

 

[ceilingwalker]

It turns out that my 1794-AENT is intermittently losing coms and the VHSC doesn't like it.