## Questions

## Answers

**How do the units on the B&K 2635 charge amplifier work**The knobs on the front of the B&K 2635 charge amplifer are not intuitive. Here is how to calculate the effective calibration factor in units of V / Engineering Units,

`Sp = ( A * 0.001 * B ) / C`

where

`A`

is the sensitivity selected on the dial in mV / Unit Out`B`

is the exponent which is the multiplier between the actual sensitivity of the transducer and the sensitivity that was entered on the three dials on the top of the charge amplifier`C`

is the Unit out selected with the Acc – Vel – Disp knob.

For example, if you have a transducer with a sensitivity of 67.2 pC / m/s^2. You enter a sensitivity on the charge amplifier of 0.672 (with the switch on the left hand side in the up position indicating 0.1 – 1). The gain dial is set to 1000 mV / Unit Out. You are measuring acceleration and the units out are 1 m/s^2 and high pass of 0.2Hz. Entering this data into the equation for `Sp`

yields

`A = 1000`

(gain setting on the mV/UO knob)

`B = 100`

(exponent for sensitivity of transducer)

`C = 1`

(Units Out setting from lower left knob)

Hence

`Sp = 1000 x 10^(-3) x 100 / 1`

`Sp = 100`

The level in engineering units is obtained by dividing the voltage by Sp

`EU Level = (Measured Volts) / Sp`

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