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Instrumentation - PM/04

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Captures & Retains Peak Value of Transients Automatic Polarity Indication 20usec Pulse width for-1dB Error • 4½ Digit Display • 3 Ranges to 19.990g

Mechanical impulse testing of structures and materials may call for instrumentation recording peak values of input and response.

The PM/04 peak hold meter retains a transient peak, or the maximum of a series of transients, as a 4 ½ digit with sign display. The reading is retained whilst the meter is powered up.
Input to the PM/04 is likely to be a signal representing acceleration, derived from a charge amplifier.

Certain facets of the input signal impinge on the operation of the PM/04 and should therefore be highlighted: 1) A fullscale reading of 19990g requires a maximum 0.5mV/g input signal (Vs = ±15V). A 1mV/g I/P limits the peak g ±15V to approx 12000g.

Both input sensitivities require rescaling of the CA/04 charge amplifier (std. 10mV/g).
Normalising the CA/04 to 10 or 20 X the accelerometer charge sensitivity, max 11 or 5.5pC/g, will meet the criteria.

2) Errors arise due to impulse waveform duration and risetime. A finite capture time is required, a 20µsec wide rectangular pulse equates to a 10% reduction in peak reading.
Fast risetime signals input to the charge amplifier may cause current limiting. A resistor placed in series with the transducer limits peak current at source. This latter introduces a risetime constraint but somewhat less than PM/04 capture time.

Slow risetime signals are subject to the charge amplifier’s minimum frequency constraint.

3) Impulse signals inherently include microphony and may therefore require lowpass filtering to recover the underlying transient.