Lake Shore 218S, User Manual

Page: 102 / 112

Lake Shore Model 218 Temperature Monitor User’s Manual
7-12 Service
PROCESS: Adjust the four current source calibration pots on the Model 218 main board until each
of the 4 inputs display exactly 2.0000 V.
7.13.9 250 Ω Input Gain Calibration
PURPOSE: To determine the input gain errors when the input is configured for 250 Ω input and
provide gain calibration constants back to the Model 218.
CONFIG: Attach the precision 250 Ω resistors to each input of the group. Be sure to connect the
resistors using proper 4-lead connection techniques. Input group configured for 250 Ω
input, all inputs of the group are enabled.
PROCESS: Via the interface obtain the RAWAD value of the 1
st
input. To determine the calibration
constant add the 250 Ω range zero offset constant to the value read and divide 250 by
that value or 250/(RAWAD r zero offset constant). For example, if the value
read was 2.48540 and the zero offset constant was 0.00005 the gain calibration
constant is 250/2.48545 = 100.585.
This gain calibration constant is provided back to the Model 218 using the GCAL
command for the 1
st
input of the group only. The above process must be repeated for
the remaining 3 inputs of the group. Once gain calibration constants for all ranges have
been determined and provided back to the Model 218 the CALSAVE command is
issued to save the constants in the E
2
prom.
7.13.10 500 Ω Input Gain Calibration
PURPOSE: To determine the input gain errors when the input is configured for 500 Ω input and
provide gain calibration constants back to the Model 218.
CONFIG: Attach the precision 250 Ω resistors to each input of the group. Be sure to connect the
resistors using proper 4-lead connection techniques. Input group configured for 500 Ω
input, all inputs of the group are enabled.
PROCESS: Via the interface obtain the RAWAD value of the 1
st
input. To determine the calibration
constant add the 500 Ω range zero offset constant to the value read and divide 250 by
that value or 250/(RAWAD r zero offset constant). For example, if the value
read was 1.24887 and the zero offset constant was 0.00009 the gain calibration
constant is 250/1.24896 = 200.166.
This gain calibration constant is provided back to the Model 218 using the GCAL
command for the 1
st
input of the group only. The above process must be repeated for
the remaining 3 inputs of the group. Once gain calibration constants for all ranges have
been determined and provided back to the Model 218 the CALSAVE command is
issued to save the constants in the E
2
prom.
7.13.11 7.5 k Ω Input Gain Calibration
PURPOSE: To determine the input gain errors when the input is configured for 7.5 k Ω input and
provide gain calibration constants back to the Model 218.
CONFIG: Attach the precision 5 k Ω resistors to each input of the group. Be sure to connect the
resistors using proper 4-lead connection techniques. Input group configured for 7.5 k Ω
input, all inputs of the group are enabled.
PROCESS: Via the interface obtain the RAWAD value of the 1
st
input. To determine the calibration
constant add the 7.5 k Ω range zero offset constant to the value read and divide 5000
by that value or 5000/(RAWAD r zero offset constant). For example, if the
value read was 1.66552 and the zero offset constant was -0.00010 the gain calibration
constant is 5000/1.66542 = 3002.24.
This gain calibration constant is provided back to the Model 218 using the GCAL
command for the 1
st
input of the group only. The above process must be repeated for
the remaining 3 inputs of the group. Once gain calibration constants for all ranges have
been determined and provided back to the Model 218 the CALSAVE command is
issued to save the constants in the E
2
prom.