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special considerations
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High source capacitance may degrade the performance of the 422E (source capacitance is the input
capacitance defined as transducer capac cable capacitance). In particular, noise may increase
and high frequency response may decrease if source capacitance exceeds the recommended level. In
some cases, low frequency oscillation of the output may occur. The maximum recommended level in
pF’s is determined using the following formula:
maximum recommended source capacitance = 10,000/422E sensitivity in mV/pC
For example, the level for a 422E02/E12 would be 10,000/10 pF = 1,000 pF, and the level for a
422E03/E13 would be 10,000 pF. If PCB 003 type low noise cable is used, these values correspond to
10 meters and 100 meters of length respectively.
422E series models for use with high temperature sensors
The 422E35 (1 mV/pC) and 422E36 (10 mV/pC) have been specifically designed to operate with the
lower insulation resistance values which piezoelectric sensors may exhibit when subjected to very high
temperatures (generally greater than 500
°
F). Both units will operate with insulation resistances as low
as 10k
Ω
.
Note: Because of the special circuitry required, the 422E35 and 422E36 have somewhat higher noise
and longer turn on time than the equivalent units designed for use with sensors with high insulation
resistance (the 422E03 and 422E02 respectively). Consult the specifications for details.
Caution! Excessive accumulated charges on the input cables can destroy the field effect transistor
(FET) in the amplifier. These charges can be grounded by shorting the center pin on the cable
connector plug to its knurled nut with any metallic object.
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