The M72 uses the bias voltage for an IEPE functional check. Sensor errors are indicated as fol-
lows:
•
quick flashing (ca. 4 Hz) of white LED: IEPE bias voltage < 1 V
→ short circuit in the sensor cable or sensor
•
slow flashing (ca. 1 Hz) of white LED: IEPE bias voltage > 20 V
→ open input or disconnected cable
4.2.1. Switching Off the IEPE Power Supply
In some cases it may be necessary to switch off the IEPE constant current supply in order to use
the IEPE input as a regular AC input. In this case, press the “Input” button repeatedly until the
blue and white LEDs switches off.
The input resistance of the amplifier is approximately 10 MΩ.
5. Amplifier
The M72 Series instruments have the following gain ranges:
Charge mode:
0.1 / 1 / 10 / 100 / 1000 mV/pC
IEPE mode:
1 / 10 / 100 / 1000 times or 0, 20, 40 and 60 dB.
The gain can be selected using buttons “Gain +” and “Gain -”.
After switching the input the lowest amplification is automatically configured.
After connecting a sensor and sometimes after changing the measuring range, the amplifier
needs a certain settling time because of short term overload. In this case it may take up to
30 seconds until the output voltage is free from DC components.
The amplifier output is buffered and DC coupled. Potential offset currents, which may subse-
quently be fed into the amplifier output by equipment such as a PC data acquisition board, do
not cause a DC offset at the output.
8
Figure 5: IEPE Sensor Modulation Limits
Max. output voltage =
supply voltage of
constant current source
Min. output voltage =
saturation voltage
(see data sheet)
Sensor bias voltage
(see data sheet)
negative overload
0V
positive overload
24 V
0.5..1 V
5 .. 14 V