Raspberry JAM To Sensor, Gain Question

#1

JAM attenuation resistors R[a] and R[b] are based on signal input level.

If signal input is +/-10 volts relative to ground, (a 40 volt differential signal), R[a] is recommended as 33K and R[b] is 12K.

If input signal is below an absolute span of 3 volts R[a] and R[b] are shorted out.

My sensors are Dave Nelson’s FMES (Fluid Mass Electrolytic Seismometers). The sensor second amplifier stage provides a voltage gain of 40 to provide +/-10 volts relative to ground.

Can’t I reduce the sensor second stage gain so I reduce the signal to below an absolute span of 3 volts? This should allow me to short out R[a] and R[b].

How does a “signal +/-10 volts relative to ground” compare to “an absolute span of 3 volts”? What reduction in gain is required to go from the higher to lower level?

thanks,

Bob

#2

Hi Bob,

Our technical support policy states that JAM-related electrical engineering questions are beyond the scope of what our staff can provide as free community-based support. Our hardware experts are very good at what they do, but they are in high demand.

If you are in the process of making a JAM purchase and would like customized setup for the specific instrument you will use, you may add this service to your order at checkout time: https://shop.raspberryshake.org/product/raspberry-jam-universal-digitizer-customization/

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You are also welcome to seek the advice of the community at large. Thank you for understanding, and I apologize for any inconvenience this may cause.
Ian