Lake Shore 234, User Manual

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Lake Shore Model 234/234D User’s Manual
Operation 3-3
3.3 OUTPUT TO LOG(R) CONVERSION
When no CalCurve is present, set the T/R switch to R . The output current or
voltage are directly proportional to the log of the resistance reading. This is
the transmitter output for both the Model 234 and 234D. Only the display of
the Model 234D is resistance only.
If the 4 – 20 mA output is used, the current is calculated by:
where I
OUT
is the current measured from the Model 234. Use the following
formula to convert the output current to resistance:
For the 0 – 20 mA output, the current is calculated by:
where I
OUT
is the current measured from the Model 234. Use the following
formula to convert the output current to resistance:
If the 0 – 10 V output is used (with a 500
Ω
±0.02% output load resistor), the
following formula is used to compute the voltage:
where V
OUT
is the voltage measured from the Model 234. Use the following
formula to convert output voltage to resistance:
Example: If the I/V OUT switch is in the I position (4 - 20 mA out), the
output is 4 mA for the log(R) equal to 0 (1
Ω
) and 20 mA for the log(R) equal
to 6 (1 M
Ω
). A resistance of 1 k
Ω
results in an output of 12 mA (log(R) equal
to 3). If input resistance is greater than 400 k
Ω
, output is 0 current. A
resistance greater than 400 k
Ω
is considered an open and 0 current is used
as an alarm indication for a 4 - 20 mA loop. If the I/V OUT switch is in the V
position (0 - 20 mA out), output is 0 mA for the log(R) equal to 0 (1
Ω
) and
20 mA for the log(R) equal to 6 (1 M
Ω
). A resistance of 1 k
Ω
results in an
output of 10 mA (log(R) = 3.