Putting it all in one Case?

[vid1900]

I have a big metal computer server case.

Is there any problem in putting the:

Computer Mother Board
PMDX-126
PMDX-134
Stepper Power Supply
Geckos 203v (all mounted on big aluminum heat sink)

All in the same case?

Do any of the grounds need to be isolated, or is it actually better to have them all sharing the same grounded box?

[vid1900]

Or I guess another way of asking is, if I take 12v from the computer hard drive cable to power my proximity sensors, am I dangerously defeating the voltage isolation on the PDMX126?

[ger21]

A quick look at the manual shows that the PMDX-126 can supply the 12V for your sensors. There are two diagrams in the manual. One for using the onboard 12V, and one for using an external power supply. There's also a note that about defeating the isolation

[vid1900]

A quick look at the manual shows that the PMDX-126 can supply the 12V for your sensors. There are two diagrams in the manual. One for using the onboard 12V, and one for using an external power supply. There's also a note that about defeating the isolation

Right, but my manual has a note that says for most reliable operation, use an external, regulated power supply for the sensors.

The 12V supply from the computer is VERY regulated @ 12.01V

[ger21]

Right, but my manual has a note that says for most reliable operation, use an external, regulated power supply for the sensors.

Doesn't that note say to use a 24V power supply? And the diagram above the note shows how to wire it. The ground from the external supply goes next to the input pin.

I'd ask Steve at PMDX if you can use the PC supply and still maintain isolation.

[vid1900]

Doesn't that note say to use a 24V power supply?

My sensors say 9-20 volts so I figured 12v would be fine

I'd ask Steve at PMDX if you can use the PC supply and still maintain isolation.

I was hoping he or someone else who knows would chime in on the discussion. Hate to call him on a holiday weekend.

[Al_The_Man]

Just a look through the manual it would appear that the input is NPN compatible opto-isolated In so if you were to use your PC 12v you would connect the PC common and 12v+ to the prox, then connect the PC common and prox output to the BOB common and the input respectively, the PC 12v+ would not be connect to the BOB.
Keep in mind your PC 12v common is going to be at earth ground.
Al.

[vid1900]

Thank you Al for the quick response.

The entire PC case is going to be at earth ground, so the Gecko case (connected to the heatsink) will be also.

So, leading back to my OP, will everything sharing the same ground be a problem or a plus?

[Al_The_Man]

I have always gone with commons at earth ground where permitted or possible.
With the service ground tied to the central point.
Al.

[morestuff]

Sorry to be late joining this thread.

Every NPN proximity sensor that we have tested has worked
fine with the power supplied by the PMDX-126.

In the case PNP style sensors, we recommend operation from
a 24 VDC power supply and since the PMDX-126 only offers
12 VDC, this power must come from an external supply.

In any case we recommend that if an external power source
is used, it should be isolated from the computer power system
in order to not mix the ground systems between the computer
and the CNC machine. This of course precludes using the
computer power supply for the sensors. There is no reason
to use the computer supply for sensors because it is only
12 VDC which is insufficient for PNP sensors, and the PMDX-126
supply is already suitable for NPN sensors.

In the end, both the computer ground and the machine ground
should be connected to the safety ground. The point is to be
sure that each piece of the system has only ONE path to the
safety ground so that ground loops are not possible.

Steve Stallings
www.PMDX.com