5.8 Curve Numbers and Storage
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5.8 Curve
Numbers and
Storage
The Model 335 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 335 has 39 user curve locations, numbered 21 through 59. Each location
can hold from 2 to 200 data pairs (breakpoints), including a value in sensor units and
a corresponding value in kelvin. Using fewer than 200 breakpoints will not increase
the number of available curve locations. SoftCal™-generated curves are stored in
user curve locations.
5.8.1 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
15 characters can be entered from either the front panel or from the computer
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 5-3.
Curve header parameter
Format
Description
Sensor units
full scale range
Sensor units
maximum resolution
V/K
Volts vs. kelvin
10 V
0.00001 V
)
/
K
Resistance vs. kelvin for
platinum RTD sensors
10 K
)
0.001
)
Log
)
/K
Log resistance vs. kelvin for
NTC resistive sensors
4 log
)
0.00001 log
)
mV/K
Millivolts vs. kelvin for
thermocouple sensors
±100 mV
0.0001 mV
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. 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 335
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.
5.8.2 Curve
Breakpoints
Temperature response data of a calibrated sensor must be reduced to a table of
breakpoints before entering it into the instrument. A curve consists of 2 to 200 break-
points and each breakpoint consists of one value in sensor units and one temperature
value in kelvin. The Model 335 uses linear interpolation to calculate temperature
between breakpoints. The instrument will show T.OVER or T.UNDER on the display if
the sensor reading is outside the range of the breakpoints. Sensor units are defined by
the format setting in TABLE 5-3.
TABLE 5-3
