PCB Piezotronics R480E09, Инструкция по установке и эксплуатации, Страница: 11 / 18

PAGE 6
MANUAL NUMBER: 19175
MANUAL REVISION: B
Figure 4: Diagram: AC Coupling
If the sensor amplifier and/or cable are damaged to short open, the meter will indicate in the full scale (yellow)
area. Should the sensor amplifier and/or cable be damaged to short closed, the meter will indicate zero volts (red
area). Immediately after connecting readout instrument, (oscilloscope, meter, recorder, etc.) to the output jack,
the 47
µ F coupling capacitor will begin charging through the internal resistor and input resistance of the readout
instrument. This charging will cause an apparent “drifting” of the output signal until the capacitor is fully charged.
Such drifting is considered normal operation.
Coupling Time Constant (TC), AC Coupled
The coupling discharge time constant (DTC) is the
product of the capacitor (47
µ F) and the parallel internal
resistor and the input resistance of the readout
instrument (See Figure 4, Equation 1).
Equation 1
:
TC (sec) = C
c
(microfarads) x R
in
(ohms)
The small amount of leakage through the 47 µ F coupling capacitor will typically result in a +30 mV maximum offset
with a 1.0 megaohms readout load. Normally, it is desirable to keep the coupling discharge time constant (DTC)
long with respect to the sensor discharge time constant to minimize the effect of the coupling distance time
constant on low frequency response. Typical coupling discharge time constants for various values of readout
input resistance are shown in Table 1.