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5.6 Curve Numbers and Storage 113
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5.6 Curve
Numbers and
Storage The Model 372 has 20 standard curve locations, numbered 1 through 20. At present,
not all locations are occupied by curves; the others are reserved for future updates. If
a standard curve location is in use, the curve can be viewed using the view operation.
Standard curves cannot be changed by the user, and reserved locations are not avail-
able for user curves.
The Model 372 has 39 user curve locations, numbered 21 through 59. Each location
can hold from 2 to 200 data pairs (breakpoints), including a value in ohms, a corre-
sponding value in kelvin, and a corresponding curvature value that is only used for
cubic spline curves. If a linear curve is loaded, the curvature value is set to zero. Using
fewer than 200 breakpoints will not increase the number of available curve locations.
5.6.1 Curve Header
Parameters Each curve has parameters that are used for identification and to allow the instru-
ment to use the curve effectively. The parameters must be set correctly before a curve
can be used for temperature conversion or temperature control.
D
Curve number: 1 to 59.
D
Name: defaults to the name “User Curve” for front panel entry. A curve name of up
to fifteen characters can be entered from either the front panel or from the com-
puter interface. Refer to section 4.2.3 for alpha-numeric entry.
D
Serial number: a sensor serial number of up to ten characters (letters or numbers)
can be entered from either the front panel or from the computer interface. Refer
to section 4.2.3 for alpha-numeric entry. The default is blank.
D
Format: the format parameter tells the instrument what breakpoint data format
to expect. Different sensor types require different formats. Formats for
Lake Shore sensors are described in TABLE 5-2.
D
Setpoint limit: limits the control setpoint to values less than or equal to this set-
ting. A setpoint limit can be included with every curve. The default is 375 K. Enter
a setting of 9999 K if no limit is needed.
D
Temperature coefficient: the temperature coefficient is derived by the Model 372
from the first two breakpoints. The user does not enter this setting. If it is not cor-
rect, check for proper entry of the first two breakpoints. A positive coefficient
indicates that the sensor signal increases with increasing temperature. A
negative coefficient indicates that the sensor signal decreases with increasing
temperature.
Format Interpolation method Description
Sensor units
full scale range
Sensor units
maximum resolution
)
/K Linear
Resistance vs. kelvin for
platinum RTD sensors
10 M
)
0.00001
)
Log
)
/K Linear
Log resistance vs. kelvin for
NTC resistive sensors
10 log
)
0.00001 log
)
)
/K Cubic spline
Resistance vs. kelvin for
all RTD sensors
10 M
)
0.00001
)
TABLE 5-2 Curve header parameter