Lake Shore 372, Руководство пользователя, Страница: 101 / 214

4.5 Instrument Setup 89
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Once the input is configured (section 4.4), you may choose a temperature curve. Any
standard or user curve that matches the format of the sensor type configured for a
given input will be available under the curve parameter in the Input Setup menu for
that input. You are also given the choice of “none.” When set to “none,” front panel
readings configured for kelvin will display the NOCURV message and the interface
will report 0 K for KRDG queries.
Menu navigation:
Input Setup
Q
Input (A, 1-16)
Q
Curve (Any curve of RTD type)
4.5 Instrument
Setup
The parameters grouped under Instrument Setup apply to all input channels whether
or not a scanner is installed.
4.5.1 Frequency
Selection The Model 372 AC measurement input runs at a nominal excitation frequency of
13.7 Hz. This frequency was chosen so that it and its harmonics are separated from
both 50 Hz and 60 Hz line frequency. It was also chosen to balance the effects of set-
tling time and cable capacitance. It may be necessary to change the frequency to
avoid interaction between this instrument and other measurements. This is some-
times necessary when two or more bridges are used in the same system. The Model
372 offers four alternate nominal frequencies of 9.8 Hz, 11.6Hz, 16.2 Hz, and 18.2 Hz,
with the control input by default being assigned 16.2 Hz. Frequency can be changed
through firmware without turning the instrument off; however, the hardware must
be allowed to settle before new readings are valid.
While running the measurement input and control input in parallel, we recommend
using different excitation frequencies for each input. This is to avoid an offset that will
occur in the reading as a result of the two inputs coupling together. The offset
becomes significant when the current levels between the two input excitations differ
by a factor of 100 or more (i.e., the control input set to 1 nA and the measurement
input is set to 100 nA).
A frequency “beating” will occur when the two inputs are set to different frequencies.
However, this “beating” is easily removed by filtering the respective readings.
Menu navigation:
Instrument Setup
Q
Measurement Input (9.8 Hz, 11.6 Hz, 13.7 Hz, 16.2 Hz, 18.2 Hz)
Default: 13.7 Hz
Interface command:
INTYPE
Menu navigation:
Instrument Setup
Q
Control Input (9.8 Hz, 11.6 Hz, 13.7 Hz, 16.2 Hz, 18.2 Hz)
Default: 16.2 Hz
Interface command:
INTYPE
15 Reserved — — — —
16 Reserved — — — —
17 Reserved — — — —
18 Reserved — — — —
19 Reserved — — — —
20 Reserved — — — —
21 to 59 User curves — — — linear or cubic spline
*Instrument may not support the sensor over its entire range
Curve
number
Curve name Sensor type Model number Temperature range* Interpolation method
TABLE 4-8 Sensor curves