AD598: Multiple LVDTs

Document created by analog-archivist Employee on Feb 23, 2016
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I would like to know if I can use the AD598 to condition a signal in range of
10meters. I need to operate six LVDT units with one AD598. I will switch
between LVDT in each measrement. Please advice on The 10 meter and about the
switching chip.


1. Drive current of the excitation outputs. Depending on the current
requirements of the
LVDT that you are using you may need to buffer the excitation outputs.

2. You can use a low Ron Multiplexers. The max frequency its going to see is
20kHz. It could
be a lot lower depending on what excitation frequency you are using. The max
amplitudes it should see is 3.5Vrms, but again this will depend on the

3. The 10m long wire should not be a problem as the part is ratiometric. The
main thing would be to try and ensure that the returning signals are all
treated the same i.e. same length of wires, same Ron through the Mux. This
prevent errors.

4. Settling time of the amplifier. As you are swapping between the LVDTs,
settling time might be an issue. It depends on how different the plant stem
diameter measurements are. We don't spec settling time as it depends entirely
on the customers choice of excitation frequency and bandwidth. But just to give
you an idea, typical figures for settling time would be

Excitation freq Bandwidth Sett. time
400Hz                 40Hz 26ms
800Hz                 80Hz 15ms
2.5kHz                 250Hz 7.5ms