- #1
rutman
- 3
- 0
hi
i am using a lockin amplifier for the 1st time other than a canned college lab demo.
i have a 5mV signal from a strain gage that is driven with 10Vpp at 1kHz or whatever i choose.
the 5mV is increased to 5.01mV when i add some weight to the arm the
gage is weighing.
i wanted to increase sensitivity of this reading with the LIA since there is noise in the next digit, i.e.
i read 5.01mV +- 0.01mV.
But i seem to go out of range (overload) before reading any weight change.
do i need to get a 0V average signal first, and put this into
the LIA?
the 4 strain gages are in a full wheatstone bridge configuration.
The 10V 1kHz signal is sent to the bridge and to the LIA 'reference' input,
5mV 1kHz bridge output sent to to LIA signal in. I adjust the LIA phase for max output,
zero the signal with the internal LIA offset, and increase sensitivity until i overload.
then i back off the sensitivity so there's no overload. at this point i see no change in output
with change in weight. the LIA sensitivity is generally 30mV at this point, whereas
the signal I want to measure is 0.01mV or less, so it seems natural i won't get a change in
output. the only thing i can think of is i must 'balance the bridge' to get 0.00V output, and
amplify this to higher levels e.g. at the 0.01mV level.
is this right?
i am using a lockin amplifier for the 1st time other than a canned college lab demo.
i have a 5mV signal from a strain gage that is driven with 10Vpp at 1kHz or whatever i choose.
the 5mV is increased to 5.01mV when i add some weight to the arm the
gage is weighing.
i wanted to increase sensitivity of this reading with the LIA since there is noise in the next digit, i.e.
i read 5.01mV +- 0.01mV.
But i seem to go out of range (overload) before reading any weight change.
do i need to get a 0V average signal first, and put this into
the LIA?
the 4 strain gages are in a full wheatstone bridge configuration.
The 10V 1kHz signal is sent to the bridge and to the LIA 'reference' input,
5mV 1kHz bridge output sent to to LIA signal in. I adjust the LIA phase for max output,
zero the signal with the internal LIA offset, and increase sensitivity until i overload.
then i back off the sensitivity so there's no overload. at this point i see no change in output
with change in weight. the LIA sensitivity is generally 30mV at this point, whereas
the signal I want to measure is 0.01mV or less, so it seems natural i won't get a change in
output. the only thing i can think of is i must 'balance the bridge' to get 0.00V output, and
amplify this to higher levels e.g. at the 0.01mV level.
is this right?
