Lake Shore 372, User Manual, Page: 126 / 214

114 c
HAPTER
5: Advanced Operation
Model 372 AC Resistance Bridge and Temperature Controller
5.6.2 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, one temperature
value in kelvin, and one curvature value scale factor used for cubic spline interpola-
tion. The Model 372 uses either linear or cubic spline interpolation to calculate tem-
perature between breakpoints, depending on the format of the curve. 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 5-2.
Breakpoint setting resolution is six digits in temperature. Most temperature values
are entered with 0.001 resolution. Temperature values of 1000 K and greater can be
entered to 0.01 resolution. Temperature values below 10 K can be entered with
0.0001 resolution. Temperature range for curve entry is 0 K to 9999.99 K.
Setting resolution is also six digits in sensor units. The curve format parameter
defines the range and resolution in sensor units as shown in TABLE 5-2. The sensor
type determines the practical setting resolution. TABLE 5-3 lists recommended sen-
sor units resolutions.
Enter the breakpoints with the sensor units value increasing as point number
increases. There should not be any breakpoint locations left blank in the middle of a
curve. The search routine in the Model 372 interprets a blank breakpoint as the end of
the curve.
The curvature parameter is always six digits in resolution. It is a scale factor that is
used to calculate the four coefficients of the cubic spline polynomial. When loading a
curve of a linear format, this value is automatically set to zero by the Model 372.
Sensor type
Typical Lake Shore
model
Format Limit (K)
Temperature
coefficient
Typical sensor
resolution
Platinum 100 PT-100
)
/K 800 Positive 0.001
)
Platinum 1000 —*
)
/K 800 Positive 0.01
)
Rhodium-iron RF-800
)
/K 325 Positive 0.001
)
Carbon-glass CGR-1-1000 log
)
/K 325 Negative 0.00001 log
)
Cernox® CX-1050 log
)
/K 325 Negative 0.00001 log
)
Germanium GR-200A-100 log
)
/K 325 Negative 0.00001 log
)
Rox™ RX-102A log
)
/K 40 Negative 0.00001 log
)
*Not offered by Lake Shore
TABLE 5-3 Typical curve parameters