Output to Input speed.

ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I've done small scale PLC for 40 years or so and this is the first time I've had an input fail. Voltage to it but no response. I've been using a two second delay to flag a coil failure, which is fine once up and running. I changed it to one second but feel I could make it even less.

PLC output to an interposing relay that then controls a starters 480v coil. Input back to the PLC via the starter's aux contacts. Any educated guesses as too how long that should take? IIRC program scan time is about 10 milli second. I'm not worried about contact bounce.
 
I'd be sure that the delay is at least twice as long as your scan time. But your first sentence talks about an input failure, or do you mean a logic failure?
 
TwoBlocked said:
I'd be sure that the delay is at least twice as long as your scan time. But your first sentence talks about an input failure, or do you mean a logic failure?
Click to expand...
The actual PLC input failed to respond to the applied voltage. A new card solved the problem. My logic flagged the issue as a missing input but it took a bit to figure out it had failed.

I asked ADs PLC forum and the guys there responded with pickup times varying due to size, age, humidity etc. (Duh…well I forgot.)
 
Tom,

So you want to understand how long it takes for the output command to input "round-trip" time?

If you own the code and have the time onsite to experiment, you can use the PLC itself to measure the time it takes from the command to close the relay to the input sensing the aux contact closing.

1000 pardons if that's not what you wanted to know.
 
MD Automation said:
Tom,

So you want to understand how long it takes for the output command to input "round-trip" time?

If you own the code and have the time onsite to experiment, you can use the PLC itself to measure the time it takes from the command to close the relay to the input sensing the aux contact closing.

1000 pardons if that's not what you wanted to know.
Click to expand...
Not onsite, it is my code but not a concern now.
 
MD Automation said:
Tom,

So you want to understand how long it takes for the output command to input "round-trip" time?

If you own the code and have the time onsite to experiment, you can use the PLC itself to measure the time it takes from the command to close the relay to the input sensing the aux contact closing.

1000 pardons if that's not what you wanted to know.
Click to expand...
Dad gummit!! Now I'll need to give it a shot. I do have a PLC that controls my Air Compressor. With a bit of rearranging and adding a couple wires, I can do it.
 
ptonsparky said:
Dad gummit!! Now I'll need to give it a shot.
Click to expand...

Do it, just for the fun of it !!

Obvs I don't know what PLC and/or software you are using. And to trap the time between output command and input sensor change is easy to do by hand in the PLC code itself. But many manufactures offer some kind of Oscilloscope function so that you can record and later look at any of the variables used in the PLC program. You can see when they come on and off, and directly measure the time between state changes.

You (Tom) likely know this already, but I thought to mention it for others here that do not dabble much in the PLC world. The ability to record and look at, later on, program variables is amazingly useful. You can see very similar tools now in the automotive world, with products like a PICO scope. 4 or 8 channels of recording, that you can analyze "off-line" to look at nearly anything electrical on the car. Like are you missing pulses from the Crankshaft sensor. Or what the voltage level of any ECM input or output is. Really cool stuff.
 
You must log in or register to reply here.
Top