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-15V
4
PSI System Controls and Diagnostics
3
V-
4k7
2
1
V+
8
Input (1 of 8)
+15V
Figure 21. M40 analog input configuration (referenced to AGnd).
The signals then pass through a two-pole low-pass analog filter with a -3dB point at 10 kHz and
a gain of 0.50, before being delivered to the ADC.
Figure 22. M40 analog input filter response.
The multichannel ADC is fully bipolar, +/- 5V range with 16 bit resolution. All eight inputs are
sampled simultaneously at 250 kHz and accumulated in the averaging buffer of the FPGA. The
use of averaging (downsampling) increases the effective resolution of the M40 greatly. The
amount of averaging is under software control. The PIC microcontroller applies the calibration
to convert to floating point values in volts.
The eight identical analog outputs are generated by a 16-bit DAC, offset to give an analog value
centred on 0.0 V, and passed through an output stage with gain 2.01 to give a certain -10 to +10
V range. A 100 ohm series resistor in the feedback loop protects against external short circuits.
M40 User Manual
M40_UM_150226
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