Spectrum Controls 140 AUI 040 00sc - Manual (Page 28)

16-Channel Universal Analog Input Module
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3x+0 . . . 7 Over Range Flag: Bit 5
This is a nonfatal over range flag. The bit is set to “1” when an input value is read within one count of the
maximum range value. When the input value is within normal limits the flag is automatically reset to “0.”
3x+0 . . . 7 Configuration Error Flag: Bit 6
The calibration error flag is a fatal error. When the flag is set to “1” there is a configuration mismatch.
Configuration errors include any illegal configuration, such the selection of an unsupported format or filter
option, or configurations that must be the same for all channels within a group of channels.
3x+0 . . . 7 Calibration Error Flag: Bit 7
The calibration error flag is a fatal error. When the flag is set to “1” the ADC cannot calibrate within specifi-
cations.
3x+0 . . . 7 Temperature Units Echo: Bit 8
3x+0 . . . 7 Fault Detect Echo: Bits 9-10
3x+0 . . . 7 Format Echo: Bit 11-12
3x+0 . . . 7 Filter Echo: Bit 13-14
3x+0 . . . 7 Resistance Range Echo: Bit 15-16
RTD Fault Detection
The module can detect both RTD open circuits and shorts. This works as follows:
· Open positive excitation. The S/W will read positive full scale. This will be flagged as a bad input.
Reading will default to the full-scale value for the range selected. Note that S/W can detect an over-
range which is not an open input.
· Open negative excitation. Reading will be 0. This will cause the reading to be flagged as a bad input.
Value read will be negative full scale for the range selected.
· Open high signal. The module switches in the reference voltage prior to reading the RTD voltage. This
charges the filter capacitor downstream of the input multiplexer. If the input is open, This capacitance
will charge the filter capacitor upstream of the multiplexer input. This will cause the reading to eventu-
ally go to positive full scale and will be flagged as a bad input as it is when ther is an open positive
excitation. Note that this capacitive charging process may take several updates. This method is not
designed to instantly flag an open wire, but to ensure it will eventually “float” high enough to be an
obvious fault. Because of input range limitations, this method does not apply to the 3000 ohm resis-
tance range or the 1000 ohm RTD ranges.
· Open low signal. If this wire opens, it will cause the input voltage read to float. If the input voltage
drifts too high or too low, a fault will be detected. Unlike the open hi signal, there is no technique
implemented to detect this type of fault.