One of our 800's seems to have developed a problem with reading BGV(6W) inputs. There seems to be a loss of resolution resulting in an increase of noisy data.

The method of input appears to be OK as the 800 module was swapped onto the terminals with our 2nd 800 showing no problems. Any theories?

Thanks,
Mitch

Good afternoon Mitch,

So the load cell is wired into the base and when you swap over the DT800 with another you have noise on one but not on the second DT800..

When you say one has more noise than the other, how much more noise are we talking about?

I assume the you ran exactly the same program on each DT800?
If you didn't then check if one has the gain lock set higher than the other.

Does the one with the noise pass the TEST command?
Did you run the same power supply with both DT800's?

Cheers,
Roger

So the load cell is wired into the base and when you swap over the DT800 with another you have noise on one but not on the second DT800..

Yes.. but it's a strain gauge input card with 10 or so strain gauges. I use the externally powered five half bridges on a channel pair method.

When you say one has more noise than the other, how much more noise are we talking about?

About +/- 500 microstrain.... as in BIG! It gets worse when unplugging the power to the laptop making me think an earth loop problem in the logger - inducing a 3000uE offset. I might ad doing the same with the "good" 2nd logger has no effect on data.

Analog inputs in the 0-10 Volt range using V(#) seem to be ok on the "bad" logger while the BGV inputs are noisy.

Both passed the "test" command and were sent the same program - the problematic logger has worked ok until just recently until an away job making me think a "knock" by your average baggage handler has caused a fault.

Mitch

Good afternoon Mitch,

Yep 500 ue is a bit excessive
If it is a ground loop then try connecting the negative side of the bridge power supply to the Ac (Analog common) terminal on the DT800.

This will give the unit a ground reference.

Cheers,
Roger

Hi Rog, thanks for replying promptly.

I did try grounding the excitation supply to the Ac analog ground on the previous job. It made no difference.

My problem is that the logger is onsite some 2000 km away and will be used again in 3 weeks on another job but at the same place. I have no means to "play" and can't chance it being a simple analog ground problem.

I need some definitive information to say that the logger is possibly at fault - as that's what I think it is after firstly trying every trick in the book and eliminating everything else but the 800.

Regards,
Mitch

Good morning Mitch,

If it is a ground loop then the connecting the AC should fix it.
If you thing the DT800 is at fault then you can return it to us to look at. There will be a cost involved so please contact your dataTaker dealer for pricing.

The problem we face is that it might be some thing that is specific to your site and unless we can duplicate the conditions it might be hard to locate the problem.

Cheers,
Roger

Thanks Roger,

I've decided to take another one with me as a backup and then allow me to try the Ac option.

My (obvious) frustration was brought about by testing the logger in between the two jobs after checking over my methodology and input method with no connection to the Ac. It tested fine... but then on the job...;-)

Maybe the importance of connecting the Ac is a little understated in the manual with regard to the BGV(6W).

Mitch

Good morning Mitch,

The clue is your using an external power supply to run the bridge.
If it was being powered from the DT800 then there can't be a ground loop.

Let me explain. All voltage readings are relative, that is, we are measuring the potential difference between two points. The power supply has one ground level and the DT800 has another. With a ground loop the two ground points are at a different potential. If you get a multi meter you should be able to read the difference. By connecting the power supply to the Ac we are connecting the two grounds and removing the potential difference.

If you were powering the system from the DT800 then there can't be a ground loop because the power supply uses the DT800 ground.

There are other sources of ground loops especially when you have break down in insulation etc. So make sure you test the meg Ohms to ground when you install your gauges.

Cheers,
Roger