Hi,

In the DT800 Manual, you suggest:
"4-Wire BGV Inputs
Use voltage-excited bridge (BGV) configurations only when the bridge is close to the DT800
(BGI configurations are usually preferred)."

Can you say what it is you clarify as "close to the DT800" and is there any way to compensate for the extra resistance in the wire if its say 25 meters from bridge to DataTaker?

Cheers
Ben

Good afternoon Ben,

The only way to compensate is to calibrate the load cells with the full length of lead wire attached then change the calibration to suit.
Current excitation (BGI) is preferred as it is not affected by the lead length.
With 4 wire Voltage excitation the lead length leads to the excitation at the load cell being less that at the instrument leading to an under estimation of the load.

Cheers

Roger

Hi Roger,

Thanks, I switched to current excitation, interestingly the PPM count changed by around 10 immediately.

I am having trouble with a fluctuating reading though, wasn't sure if maybe it just needed to be connected into analogue ground so tried that and ended up with an even worse fluctuation.

Do you have any solutions for fluctuating readings? Its unexpected as the strain gauge is sitting on the bench with no load what so ever?

Cheers
Ben

Good afternoon Ben,

When you say fluctuating reading just how much fluctuation?
You should also attach any shield to the Ch terminal and a clean the contacts and wiring.

Cheers

Roger

Hi Rodger,

The fluctuations were around 6 Parts Per Million initially but it seemed that the sensor was not getting its excitation.
I had connected it as per the BGI 4 wire instructions but there was no voltage to be read on the * & # terminals, so I hooked it up to sensor power /return with a 5 volt excitation parameter.

Now the fluctuations are from 0 to 9 parts per million.
I am not using a shielded cable, ill grab some shielded twisted pair to see if that improves, and also a amplifier and filter if not.

Does this sound like the correct path?

Cheers
Ben

Good morning Ben,

There won't be a Voltage to read on the */# terminals.
The DT800 will turn on the current (or voltage) for about 10 mSec then read the channel (Usually 20 mSec) then turn the power off, so you won't be able to read anything with a multimeter.

I recommend you use shielded twisted pair cables. The output of a load cell is measured in millionth of a volt so it can be easily swamped by external noise.

To check the underlying noise in the system hook up the load cell but link the +/- terminal with a short. This will give you a true zero and show the underlying noise.

Cheers

Roger

Great, thanks Rodger Ill try this today.
Ben