I have a bunch of transducers I need to monitor, all voltage o.p.

I need to keep 4 of the 5 input channels in independent voltage mode (1V)

This leaves the one channel to which I want to connect 3 voltage inputs using shared terminal mode (ie 1*v, 1+V etc.) all obviously sharing the same ground.

So far so good...

I'm using a 12v PSU to run the DT80 and also to power a couple of 12v relays triggered from the 3D and 4D digital outputs. The PSU negative is therefore connected to digital ground (DGND)

OK, so the question is, can I use the same PSU that's running the DT80 and the relays to power the 3 transducers I want to connect to the shared terminal voltage input? The issue Im concerned with is that by connecting the common ground to the # terminal I think I'm effectively linking analog to digital ground which I understand is a no-no?

If that's the case do I use a separate PSU for the 3 transducers with the common ground, or something else?

Good morning TeaPig,

Yes you should be able to, Because you are using the same power supply there shouldn't be a ground issue on those channels.
But DON"T connect the power supply ground to the EXT#. that will brake the channel isolation for all channels including the independent ones

Cheers
Roger

Hi Roger,

Cool. Thanks.

So I take it the common ground for that channel and the DT80 system ground are internally linked/the same thing?

Cheers

TP

Good morning TP,

Which grounds are you referring to?

There is 100 VDC isolation between the analog and digital sections and there is isolation between channels in the analog section.

When a channel is sampled the relays close and the return (In your case the # terminal) is connected to the analog ground and the Voltage between the # and the input terminal measured then the relays open again and the process is repeated for the next channel reading.

In your case as the sensor and the logger are powered from the same supply you are braking the 100 VDC isolation between the analog and digital sections but only when when the channel is being sampled. In this case there should not be a problem with ground loops because there is only one power supply.

Cheers

Roger

I was referring to the signal ground and the analog ground, your reply has answered my question. Thanks v. much

I want to connect to the shared terminal voltage input? The issue Im concerned with is that by connecting the common ground to the # terminal I think I'm effectively linking analog to digital ground which I understand is a no-no????

Hi Olinelooo,

Linking analog and digital ground together will remove isolation between analog and digital terminal and depending on your wiring it may introduce a ground loop.
Total isolation between dataTaker power and analog sensor is also preferable because analog ground can float to match common voltage.
In some analog sensor it will not create a problem, for others problem is certain.

So it entirely depends on the characteristic of analog sensor to be able to tell whether breaking isolation will create a problem or not.

Best regards,
Rudy

I think you have nothing to be worry about because you are using the same power supply there shouldn't be a ground issue on those channels....