Spectrum Controls 1769sc-IF8u - Manual (Page 41)

Chapter 3: Installation and Wiring 31
terminal block. Do not mount the remote terminal block near heat
sources, as it will cause inaccurate readings.
!
ATTENTION! Do not remove or loosen the cold junction compensating
thermistor assembly located between the two CJC terminals. The thermistor
assembly must be installed to ensure accurate thermocouple input readings on
channels configured for thermocouple. The module will operate in the thermocouple
mode, but at reduced accuracy if the CJC sensor is removed. See Determining Open-
Circuit Response (Bits 4 and 5) in chapter 4.
Calibration
The universal module is initially calibrated at the factory. The module also
has an autocalibration function.
When an autocalibration cycle takes place, the module’s multiplexer is
set to system ground potential and an A/D reading is taken. The A/D
converter then sets its internal input to the module’s precision voltage
source, and another reading is taken. The A/D converter uses these
numbers to compensate for system offset (zero) and gain (span) errors.
Autocalibration of a channel occurs whenever a channel is enabled.
You can also program your module to perform cyclic calibration
cycles, every five minutes. See Selecting Enable/Disable Cyclic
Calibration (Word 0, Bit 14) in chapter 4.
To maintain optimal system accuracy, periodically perform an
autocalibration cycle.
!
IMPORTANT: The module does not convert input data while the
calibration cycle is in progress following a change in configuration. Module
scan times are increased by up to 112 ms during cyclic autocalibration.