Section 1.7 Module Operation - Spectrum Controls 1794 User Manual

Flex™ IO Isolated Universal Input Module
1-4
Section 1.7
Module
Operation
1794 FLEX
Terminal Base Unit
User's Manual Pub. 0300231-03 Rev. A
The module measures each analog signal using a dedicated A/D converter for each
channel. The converter reads the signal and converts it as required for the type of input
selected. If thermocouples are being utilized, the module continuously samples each CJC
sensor and compensates for temperature changes at the terminal base cold junction,
between the thermocouple wire and the input terminal. See the block diagram below.
8 Channels &
24VDC PWR
Signal
Conditioning
The module is designed to support up to 8 isolated channels of RTD, resistance, voltage,
current, or thermocouple.
Thermocouple measurements utilize two cold junction compensation sensors placed at
two different locations on the terminal base unit. The location of each CJC sensor was
chosen to calculate the overall CJC error accurately for each channel. Thermocouple
support includes types J, K, T, E, R, S, B, N, and C. In thermocouple mode the 1794sc-
IF8IU will measure thermocouple and CJC voltages and convert the results to a
linearized temperature reading.
RTD support includes types Pt 385, Pt 3916, Ni 618, Ni 672, Cu 426, and NiFe 518. In
RTD and resistance mode the module will inject a constant current through the RTD or
resistor, measure the voltage across the resistance and convert to a linearized temperature
or resistance reading. The IFIU supports 2 and 3 wired RTD inputs.
When configured for current or voltage type inputs, the module converts the analog
values directly into digital counts.
8 of 8
1 of 8
ADC
MICRO-
MUX
CNTRLR
+ FLTR
Isolated PWR Supply
24 VDC
Isolation
Barrier
Backplane
COMMS