Renishaw RGH24 Reference Mark Configuration in MAX?

[Laurencej]

Hi,

I am currently working on a dual-axis system, using two Renishaw RGH24 series readheads (one on each axis). The encoders are wired so as to output A+/A- B+/B- I+/I- and are powered with 5V and GND, all via a UMI-7764. The controlling card is a PXI-7350.

The system is tuned and running well, but there is no specific "Home" or "Limit" output available from the readhead. I have fitted Renishaw adjustable "Reference Markers" to the system, and the encoders flash red when traversing the sensor, meaning they are "seeing" it.

The problem I have is getting this information back into MAX, and subsequently LabView.

Is it possible to configure MAX to use the I+/I- line as a "Home" reference, which, changes state as the readheads traverses the sensor?

Regards,

Laurence

[Jochen]

Laurence,

could you please provide a datasheet of the RGH24? I'm especially interested in the output circuitry of the I+/I- signal.
Please note, that the limit switch inputs are pulled up with a 3.3 kOhm to +5V to provide direct connectivity for mechanical limit switches.
If you connect something else to these inputs you need to make sure, that your device provides a low impedance output to be able to pull-down the board's limit switch input to a value close to 0 V in the low output state.

Kind regards,

Jochen

[Laurencej]

Hi,

Thanks for the reply, Jochen.

Please find both a data sheet and installation guide attached.

This particular encoder is available is two forms - one that uses the I+/I- lines as a reference indicator, and one that uses them for a limit switch indication. I am using the former type, as although, in our application, both are "really the same thing", the reference mark options offers us increased repeatability.

I look forward to your comments.

Regards,

Laurence

[Jochen]

Laurence,

it looks like something didn't work with the attachments. They are not there.

Jochen

[Laurencej]

Let's try again!

If this doesn't work I'll insert the web addresses to the Renishaw page where they can be downloaded...

L

[Jochen]

Now it worked.
Unfortunately the electrical specifications are quite poor in these documents, so I can't see if these devices can sink enough current to pull-down the limit switch inputs. Please a) try to get the information about the output impedance from Renishaw or b) just try it.
Connecting the signals to the limit switch inputs should be save, so the worst result of this test could be the finding that it doesn't work.

Jochen

[Laurencej]

Jochen,

Thanks for your help on this. I can now confirm that this works - I simply connected the I+ line to the HOME input...

Laurence