Z-World RabbitCore, Руководство пользователя

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76 RabbitCore RCM3600
Other possible ranges are possible by physically changing the resistor values that make up
the attenuator circuit.
It is also possible to read a negative voltage on ADC_IN0 to ADC_IN5 by moving the
jumper (see Figure B-5) on header JP7, JP6, or JP5 associated with the A/D converter
input from analog ground to VREF, the reference voltage generated and buffered by the
A/D converter. Adjacent input channels are paired so that moving a particular jumper
changes both of the paired channels. At the present time Z-World does not offer the soft-
ware drivers to work with single-ended negative voltages, but the differential mode
described below may be used to measure negative voltages.
NOTE: THERM_IN7 was configured to illustrate the use of a thermistor with the sample
program, and so is not available for use as a differential input. There is also no resistor
attenuator for THERM_IN7, so its input voltage range is limited.
Differential measurements require two channels. As the name differential implies, the dif-
ference in voltage between the two adjacent channels is measured rather than the differ-
ence between the input and analog ground. Voltage measurements taken in differential
mode have a resolution of 12 bits, with the 12th bit indicating whether the difference is
positive or negative.
The A/D converter chip can only accept positive voltages. Both differential inputs must be
referenced to analog ground, and
both inputs must be positive with respect to analog
ground . Table B-3 provides the differential voltage ranges for this setup.
Table B-2. Positive A/D Converter Input Voltage Ranges
Min. Voltage
(V)
Max. Voltage
(V)
Amplifier
Gain
mV per Count
0.0 +20.0 1 10
0.0 +10.0 2 5
0.0 +5.0 4 2.5
0.0 +4.0 5 2.0
0.0 +2.5 8 1.25
0.0 +2.0 10 1.0
0.0 +1.25 16 0.625
0.0 +1.0 20 0.500