SCB-68 and rotary encoder wiring

[JoE1205]

Hey guys,

Im new to any NI related topics but I have to use a rotary encoder (Kübler Sendix 5000) with SCB-68 in order to measure rotational speed. The problem is that I dont know how to wire the pins.

So what I tried so far:

Channel A to Pin 37 | PFI 8 / CTR 0 SOURCE

Channel B to Pin Pin 3 | PFI 8 / CTR 0 GATE

GND of the rotary encoder to Pin 4 | D GND

I didnt connect Channel "0", because I dont know about its use. Furthermore I dont know the difference between CTR SOURCE and GATE.

Furthermore not connected: Inverted versions of A,B and 0

Is there a difference between all the D GND Pins?

What is the difference between CTR SOURCE and GATE?

Am I using the right pins at all?

Thanks for the help!

[Kevin_Price]

Many things here, only time for a brief response.

What DAQ board are you using?

The D GND pins all tie together on almost all "standard" NI boards.

If you have both an A and an "A-bar" (inverse of A), you likely have the RS-422 differential version of the encoder.  (I don't read German, but could at least recognize that much from the link).

   Most common NI boards need single-ended signals rather than differential, so you may need to convert all the raw encoder signals to single-ended before connecting to the SCB-68.

CTR Source and CTR Gate are very distinct in far more ways than I can address briefly.  Most "standard" NI boards that support encoders would want you to connect A to CTR Source and B to CTR AUX.  The "O" signal would connect to CTR Gate *if* you use it.

-Kevin P

[JoE1205]

Hi Kevin,

thank you for your reply.

This encoder is a RS422 differential version, as far as I understand the datasheet (by the way, there is a translation on the page -> Datenblatt). Anyway I found an other thread with some explanation for all the CTRs, still doesnt help 😄 . For some reason my SCB68 doesnt have CTR AUX. I attached the quick reference Lable of my SCB.

The output right now, when using the connections mentioned above, result into an inverted output of the measurement. Using the inverted channels doesnt change the output. I will take some pictures later in order to show you.

[Kevin_Price]

The SCB-68 is (mostly) a terminal block.  The DAQ device is inside a PC and connected to the SCB-68 with a thick cable.

The label you showed states that it's the pinout for "E-Series Devices" which don't support quadrature encoders, thus they don't have any designated pins for such connections.   There are many other pinout labels available for other kinds of devices.  Start by exploring here.

Hmmm, well, it looks like NI has changed the format of their labels since I last looked and many devices (such as the 62xx and 63xx families) which *do* support quadrature encoders no longer identify the "AUX" pin for counters.  Here's an example of a label for a dedicated counter/timer board which *does* identify pins by counter function (source, gate, aux).

Another place you can look is in MAX.  Right-click on your specific device and select "Device Pinouts" from the context menu that pops up.

If your comment about an "inverted" measurement means that the sign is reversed + vs -, well, that's just a kinda typical thing to encounter with quadrature measurements.  The sign convention for the physical encoder signals has a 50% chance of matching the sign convention you'd like for your app.  You can fix it in hardware by swapping the A and B signals with one another or you can fix it in software by reversing the sign of all readings.

Note : In theory it's a 50% coin flip whether the sign convention works out nicely.  Experience and Murphy's Law seems to suggest it actually comes out closer to 25%...

-Kevin P

[JoE1205]

Hi Kevin,

its working, after looking for the AUX pin via device pinouts. Thank you very much!