Lake Shore Model 321 Autotuning Temperature Controller User’s Manual
1-6
Introduction
1.3 PRECISION
CALIBRATION
OPTIONS
The Lake Shore Precision Calibration Option allow the user to convert calibrated sensor data into
breakpoint pairs readable by the controller program. The Precision Calibration Option is available in
three forms. The Model 8000 loads the breakpoint pairs on a floppy disk in ASCII format for Customer
downloading. The Model 8001 puts the breakpoint pairs in a NOVRAM that is installed at the factory.
Finally, the Model 80020-05 is a NOVRAM that is installed in the field.
The Precision Calibration Option improves the specified accuracy to 0.1K or better over a given
calibration range for DT-400 Series Silicon Diode Sensors. Accuracy for other sensors depends on the
sensor type and calibration range.
A copy of the break point information containing sensor type, sensor serial number, maximum allowable
error, break point number, voltage (or resistance), temperature and temperature error is supplied. A
second sheet containing only the break point temperatures and voltages is also supplied.
The Precision Calibration Option Table is a piecewise linear interpolation based on the sensor
calibration. Optimum break points are determined by an iterative procedure using weighted linear least
squares defined by either a maximum number of break points allowed or a maximum allowable error.
The break point voltages are the values from the least squares linear equations and will therefore differ
from the calibration data. Differences between voltages from the input table and the break point voltage
are converted to a corresponding error in temperature by dividing the voltage difference by the
sensitivity. Temperature errors by this method will be considerably less than by linear interpolation
between calibration data points.
Sensor
Input
(4-Lead)
Current
Source
1
2
AC Line
A/D
Converter
16 Bits
D/A
Converter
15 Bits
Program
PROM
Heater
Output
25 Watts
Power Supply
Heater Analog/Digital
RAM for
Calibrated
Sensor Curve
Analog
Output
0-10 V, 1 mA
Differential
Input
Micro-
Controller
Display
Keypad
RS-232C
Interface
Grounds 1 and 2 represent separate isolated power supplies.
Ground 1 is connected to Earth.
C-321-1-2.eps
Figure 1-2. Model 321 Block Diagram
