Dear Sir,

we are using DT85 for measuring strain gauges (full bridge) for load measurement. when we are configuring channel 1 , 2 and 3 for BGV and not connecting any strain gauges, we are getting reference error. this implies no gauge is connected. this is ok. but when we are connecting one strain gauge to channel 1 and no strain gauge is connected to 2 and 3 channels - we are getting say

channel 1 - 1234.00
channel 2 - 1123.98 ( erroneous value- no gauge connected to this channel and it should have shown reference error)
channel 3 - reference error.

now, why channel 2 is showing a value while there is no strain gauge connected .
the reference error helps us to understand if there is a connection problem or wires broken. we have tested this with diff channels and always found at least one channels ( out of three or four channels configured for strain gauge measurement and one channel only connected with a strain gauge ) is showing erroneous value while no strain gauge connected to it.

pl help us understand and troubleshoot this issue.

Regards,
gpradipta

Hi gpradipta,

When you used BGV channel for measuring full bridge strain gauge you need to specify excitation voltage by using voltage channel (page 297 of DT8x manual).
Example:
1+V(BR,2,V)
1BGV

• BR refers that voltage value from this channel will be used for BGV, without proper reference the reading will show reference error

I recommend you to use BGI (current excited bridge) in preference to BGV (voltage excited bridge) as the first is less susceptible to noise and does not suffer voltage drop caused by cable length.

The reading that you see when there is no bridge connected was due to the static charges built up and sitting in the terminal (due to high impedance input).
This static charge will vary according to the atmosphere condition (high when dry and low when wet).

If you need to check your strain gauge connection, you may use resistance channel (e.g.: 1*R(2W)). If the value is overrange then your connection is compromised.

Best regards,
Rudy Gunawan

dear Rudy,

thanks a lot for your reply.
now we have configured our strain gauges for BGI and there are no reference errors.
but when no strain gauges are connected we are getting values such as
ch 1 890321 ppm (arbitrarily changes)
ch 2 -894.1 ppm
ch 3 -894.5 ppm
if we delete ch 1 then ch 2 becomes 780421 ppm (arbitrarily changes) and ch 3 -894.1 ppm. one ch is always showing absurd value.
however, when we connect strain gauges to the channels, they are showing correct values.

pl advise us the reason for this absurd value in one channel only and help us understand this.
thanks a lot once again for your prompt reply.

regards,
gpradipta

Hi gpradipta,

I do not really know the reason for this.
This is probably the building up static charge is finally find a way to discharge through the first channel as the reading of the channel is sequential.

Best regards,
Rudy Gunawan