Two Encoders to One Input

I have a customer looking for a device that will take two encoder signals in and then let you select between them for the output. I guess we could use a series of relays or switches but he swears he has seen a device like this before..

I have found a lot of encoder signal splitters but not any devices that I would classify as multiplexers.

Does anyone know of such a device?

Thanks

as far as i know its not possible to do this, i even just called my former co-workers at Omron tech support to see if they had a solution - and they said its not possible to tie in 2 encoders to a single plc input.

the reasion is because even if its a highspeed input - the scan time needed for the plc code to differ between the two sets of pulses would mean that every time you switched between the 2 encoders you would lose a few pulses and your position would get futher and futher out of alignment.

as far as i know you always have to have each encoder tied into its own highspeed input

I'm not looking to have both encoders attached to the input at the same time. I'm looking for a device that will let me switch between the two encoders. Sometimes they want to use encoder 1, and sometimes they want to use encoder 2.

I think I found the device:
http://www.dynapar.com/uploadedFiles/Products/Heavy_Duty_Encoders/RIM_Signal_Switcher.pdf

There is no connection diagram shown but from the description, it fits exactly what I'm talking about.

oh my mistake the way i read it - it sounded liek you wanted to wire both encoders back to the plc hahahaha silly me - -its wednesday and i wana go hommmmmmmmmmmmmme

ndzied1 said:

I'm not looking to have both encoders attached to the input at the same time. I'm looking for a device that will let me switch between the two encoders. Sometimes they want to use encoder 1, and sometimes they want to use encoder 2.

I think I found the device:
http://www.dynapar.com/uploadedFiles/Products/Heavy_Duty_Encoders/RIM_Signal_Switcher.pdf

There is no connection diagram shown but from the description, it fits exactly what I'm talking about.

Click to expand...

Lol, look at the pcb. Three double pole changeover relays, a voltage regulator and an opto isolator for the change over signal. How much are they charging?

You could build your own unit very easily (just use gold plated relay contacts)

I love the "Fail Safe" feature; ie the normally closed relay contacts!!

timbo_uk said:

You could build your own unit very easily (just use gold plated relay contacts)...

Click to expand...

At a previous employer, we did exactly that. We used a fairly common Square D plug-in "ice-cube" relay with gold contacts. It was also for an encoder selector set up and not switched while in motion, but only during set up of the machine.

Paul

Firstly, WHAT is the reason to do this? I know of some, but give a hint about the application, and WHY it's necessary.

Secondly, must this be done "ON THE FLY" (as in, while something is in motion?) or can it be done while at stop?
I ask this, because I've had many situations when we needed to use an encoder to provide feedback for a master line control drive, and another one to provide feedback during a jog operation when the master drive might be inactive.
Is the client looking for something strange? Like wanting to control by either RPM or FPM? based on a motor tach or surface tach?
What are the pulse frequencies involved? if on the fly switching is required (poor control system), then just put together a little circuit board with some AND gates on it.
What voltage levels?

Welcome to my world:

rdrast said:

Firstly, WHAT is the reason to do this?
I don't know

Secondly, must this be done "ON THE FLY" (as in, while something is in motion?) or can it be done while at stop?
Don't know for sure but probably at a stop

Is the client looking for something strange?
Pretty much my whole life

Like wanting to control by either RPM or FPM?
I don't know

based on a motor tach or surface tach?
I don't know

What are the pulse frequencies involved?
I don't know

if on the fly switching is required (poor control system), then just put together a little circuit board with some AND gates on it.
Not on your life. If I build it it's mine forever, if I sell a manufactured component, I get to blame the manufacturer.

What voltage levels?
24V Differential Line Driver +A,-A,+B,-B,+Z,-Z (Yea, one I know)

Click to expand...

This exercise has given me the knowledge to ask the customer more questions and get them the right answer. I'm hoping he wants change over at a stop and then I'll use 3 Form C Relays with gold contacts and a selector switch and be done with it.

No, thank you for the response.
But those questions need answering.
We can help you, if you have answers to the above.
Look seriously at my questions above... Ask your client. Tell me WHY, and I'll potentially give a solution, or someone here with a real brain will help ya.

OkiePC said:

At a previous employer, we did exactly that. We used a fairly common Square D plug-in "ice-cube" relay with gold contacts. It was also for an encoder selector set up and not switched while in motion, but only during set up of the machine.

Paul

Click to expand...

At my previous employer there was a machine that did this as well. Just a plain old ice-cube relay. The machine was a basic indexer punching holes in angle. While punching a hole, it would switch between the front encoder and the rear encoder so that there would be zero drop.

I didn't build the machine and I swore that it was a bad setup but the relay encoder switching never caused a bit of trouble in 10 years.

TWControls said:

...I didn't build the machine and I swore that it was a bad setup but the relay encoder switching never caused a bit of trouble in 10 years.

Click to expand...

Yeah, I did not design the circuit that way either, but discovered it during troubleshooting and found someone had plugged in a normal relay without the gold plating which eventually caused some encoder loss errors. It was just one four pole relay with Form-C contacts.

I asked myself then "why would anyone do this?", but it was the only time it ever gave any trouble on apx 15 machines that used this circuit.

IIRC, it was used to select from two different supply conveyors measuring stock into a tire building machine. It only switched when the operator emptied one roll and switched to the other let-off unit. Probably 20 times per shift.

Paul

OkiePC said:

IIRC, it was used to select from two different supply conveyors measuring stock into a tire building machine. It only switched when the operator emptied one roll and switched to the other let-off unit. Probably 20 times per shift.

Click to expand...

This one switched about once every 45 seconds all day. It was a 12VDC encoder...maybe 15VDC, so I don't know how well it would have lasted at 5VDC. Still I wouldn't say it was good setup but it is possible

I later replaced the controls for a Controllogix with a M02AE for the two encoders and tied the two channels -10 to +10VDC outputs to the drive.

For information purposes only:

http://www.tbarrelay.com/