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IM 707231-01E
Description of Operation
The 30-CH Scanner Box (sold separately) connects to the input connector of the 30-CH
Fast Digital Thermometer WE7231 using the connecting cable, and the devices under
measurement are connected to each terminal of the 30-CH Scanner Box. If the device
under measurement is a thermocouple or if you are measuring DC voltage, the input
terminals are connected using a 2-wire system. When measuring resistance or
resistance temperature detectors, a 4-wire system is used.
A scanning signal is sent through the connecting cable from the WE7231 to the 30-CH
Scanner Box, and the response from the device under measurement determines which
signals are selected for input to the WE7231.
With thermocouple or DC voltage input measurement, the input signal is modified in the
attenuator (ATT) and amplifier circuits then undergoes A/D conversion. When measuring
resistance such as in resistance temperature detectors, a constant current is given
through the connecting cable from the WE7231 to the device being measured, and in the
same manner as during thermocouple or DC voltage input measurement, the voltage
signal generated at both ends of the device being measured is input to the WE7231
where it undergoes A/D conversion. These converted digital signals are isolated in the
photocoupler and the digital data which represents the measured values is stored in
memory.
When measuring temperature, the reference junction temperature is measured using the
platinum resistance temperature detector inside the scanner box, and the CPU performs
reference junction compensation, or RJC, (this function can be turned ON/OFF) and
voltage-temperature conversion on the previously stored measurement data from the
thermocouple. These results are then re-stored. The data stored in memory can be
recalled from a PC through communications.
1.1 System Configuration and Block Diagram
