Spectrum Controls Micro800 2085-IR8-SC User Manual page 47

Chapter 3: Configuring the Micro800 Expansion I/O 2085-IR8-SC Using CCW
Index
2
3
3-Wire Method
When using the 3-wire measurement with one-side sense-wire connected, two
measurements will be executed. The first measurement acquires the reading
across the main resistance load plus the doubled lead-wire resistance value. The
acquisition rate of this measurement is based on the channel scan rate. The
second measurement acquires the reading across the main resistance load plus the
single lead-wire resistance value through the one-side sense-wire. This
measurement is triggered by a microprocessor timer happens every 60 seconds.
If any open wires happen when using this option, the timer will be reset and both
measurements will happen sequentially. Until all the open circuit conditions are
resolved, the acquisition timing of the secondary measurement will be reset back
to the 6-second timeframe. Below are the steps on running 3-wire measurement
with compensation.
Measurement I:
Measurement II:
Where �� is the injected excitation current.
Calculation:
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Where ��'
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timer.
4-Wire Method
When using the 4-wire measurement with two-side sense-wire pair connected,
the only required measurement is to measure the voltage drop across the main
resistance load. It will be converted to the corresponding temperature reading or
resistance value based on the selected Input Type. The data acquisition is
executed periodically based on the channel scan rate.
Single Measurement:
2-Wire Method
When using the 2-wire measurement with no sense-wire connected, the measured
voltage drop is across the main resistance load plus the doubled lead-wire
resistance value. No lead-wire resistance compensation is executed on this
option. The data acquisition is also executed periodically based on the channel
scan rate.
Connection Method
2-wire
Invalid
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= (��
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= ( ��
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= ( ��
+ 2��
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= ( ��
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is the previous measured lead-wire value triggered by the
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Note
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+ ��
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) − ( ��
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) − 2��
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= ��
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User's Manual Pub. 0300321-01 Rev. A
3-23
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