Spectrum Controls 1746sc-NI8u - Manual (Page 16)

4 SLC 500 ™ Universal Analog Input Module
The first four input channels (0 through 3) can receive input signals from
thermocouples, millivolt, volt, or milliamp devices. The last four input
channels (4 through 7) can receive input signals from thermocouples,
millivolt, volt, milliamp, or 2, 3 or 4-wire RTD or resistance devices. If
RTD or resistance inputs are selected, channels 4 through 7 can be
individually configured for the supported RTD or resistance types.
When configured for thermocouple input types, the module converts
analog input voltages into cold-junction compensated and linearized, digital
temperature readings. The module uses the National Institute of
Standards and Technology (NIST) linearization tables based on ITS-90 for
thermocouple linearization.
When configured for RTD input types, the module converts the analog
input voltages into digital temperature readings, based on the alpha type,
wire type, and ohms specified. The standards used are the JIS C 1604-
1997 for the Pt 385 RTD types, the JIS C 1604-1989 for the Pt 3916 RTD
types, SAMA RC21-4-1966 for the 10
Ω Cu 426 RTD, DIN 43760 Sept.
1987 for the 120 Ω Ni 618 RTD, and MINCO Application Aid #18 May
1990 for the 120 Ω Ni 672 RTD.
When configured for millivolt, volt, milliamp, or resistance analog inputs,
the module converts the analog values directly into digital counts. For
those input types, the module assumes that the input signal is linear prior to
input into the module.
System Operation
At power-up, the module checks its internal circuits, memory, and basic
functions. During this time the module status LED remains off. If the
module finds no faults, it turns on its module status LED.
After completing power-up checks, the module waits for valid channel
configuration data from your SLC ladder logic program (channel status
LEDs are off). After channel configuration data is transferred and
channel enable bits are set for one or more channels, the module turns on
its channel status LEDs. Then it continuously converts the inputs to the
data format you selected for the channel.
Each time the module reads an input channel, the module tests that data
for a fault, i.e. over-range, or under-range condition. If open-circuit
detection is enabled, the module tests for an open circuit condition. If it
detects an open-circuit, over-range, or under-range condition, the module
sets a unique bit in the channel status word and causes the channel status
LED to blink.
The SLC processor reads the converted thermocouple, RTD,
resistance, millivolt, volt, or milliamp data from the module at the
end of the program scan, or when commanded by the ladder
program. After the processor and module determine that the data
transfer was made without error, the data can be used in your ladder
program.