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Renishaw TP-20 Probe Connection

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06 Apr 2021 11:10 #205074 by andypugh
Replied by andypugh on topic Renishaw TP-20 Probe Connection
I have a number of Zeiss probes that also have a significant resistance when closed.

I have forgotten what I did to make them work, quite possibly nothing at all.
500R is quite probably low enough to pull-down a pulled-up GPIO input. Have you tried just wiring it in to see what happens?

Now, if you can tell me how to interface a TP-200 probe....

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06 Apr 2021 11:19 #205077 by jackdavies
Replied by jackdavies on topic Renishaw TP-20 Probe Connection
I have not yet tried wiring it in, I am still waiting for some spring contacts to arrive, but yes maybe it will just work and I am over complicating this haha.

However there is a strong benefit of reducing the voltage and current actually applied to the ball and pins in the probe to prevent pitting of the contacts over time. As well as an improvement in trigger repeatability.

Can the Index signal at TB3-13 be used as a 5v input? I have put the connections in the attached schematic on the left.

Thanks!
Attachments:

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06 Apr 2021 11:38 #205081 by andypugh
Replied by andypugh on topic Renishaw TP-20 Probe Connection

Can the Index signal at TB3-13 be used as a 5v input?.


Probably. Though I don't think that you have mentioned which Mesa card you are using.

The circuit shown is "NPN", depending on the interface card you are using you might want to change to "PNP". (quotes because I am using the terms loosely to mean "switch to gnd" and "switch to +V").

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06 Apr 2021 11:40 #205082 by jackdavies
Replied by jackdavies on topic Renishaw TP-20 Probe Connection
I am using the 7i76e which switches to +V as far as I know, so NPN would be the right one.

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06 Apr 2021 11:50 - 06 Apr 2021 11:51 #205083 by andypugh
Replied by andypugh on topic Renishaw TP-20 Probe Connection
7i76e is sinking inputs on GPIO.

FIELD I/O
The 7I76 has a 32 input, 16 output isolated field I/O system to support a wide range
of input and output devices. The isolated I/O is intended for low voltage DC control
systems (commonly 24VDC). Inputs are sinking type. That is they sense positive input
voltages relative to field ground. Outputs are sourcing (7I76) or sinking (7I76D) type.
Sourcing outputs supply field power to field ground referred loads. Sinking outputs ground
field voltage referred loads when on


The encoder inputs are differential, but I don't know about sourcing/sinking in that context.
Adding a differential line-driver to your circuit might be a win.
Last edit: 06 Apr 2021 11:51 by andypugh.

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06 Apr 2021 15:29 #205129 by jackdavies
Replied by jackdavies on topic Renishaw TP-20 Probe Connection
I think a transistor could work here as the grounds are shared, and then I could just input it to a standard input.

arduino.stackexchange.com/questions/508/...circuit-with-arduino

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06 Apr 2021 15:54 #205136 by andypugh
Replied by andypugh on topic Renishaw TP-20 Probe Connection
There already is a transistor, Q1.
But I think that it would be better if Q1 was between the positive field voltage and a GPIO input. If you changed to LM358 you could run the whole circuit at 24V and (with a few resistor changes) still only have 15mV at the probe contacts.

Will this circuit be at the probe end or the machine end?

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06 Apr 2021 20:08 #205176 by jackdavies
Replied by jackdavies on topic Renishaw TP-20 Probe Connection
Yes that would be perfect, would be best at the machine end. Actual probe is only 13mm dia so not much space to package other electronics haha.

Would you know how to modify the schematic to make that work by any chance?

Thanks a lot!

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06 Apr 2021 20:49 #205183 by andypugh
Replied by andypugh on topic Renishaw TP-20 Probe Connection
I know just enough electronics to be dangerous, so I would rather not advise.
I don't know if you can just connect a PNP transistor to the +V rail and still have it driven by the op-amp output as shown.

This might help:
electronicsclub.info/transistorcircuits.htm

Based on that I think it would probably work to just move the transistor and swap the type. Breadboard it first?

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07 Apr 2021 02:14 #205222 by dm17ry
Replied by dm17ry on topic Renishaw TP-20 Probe Connection
a while ago i checked the renishaw PI4 probe interface unit - it supplies the probe with 12V limited to 0.5mA. so i think some circuit with a comparator before the optoisolated machine input would be a good idea...

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