Lake Shore Model 218 Temperature Monitor User’s Manual
Service
7-13
7.13.12 5
k
Ω
Input Gain Calibration
PURPOSE: To determine the input gain errors when the input is configured for 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 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 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 2.49870 and the zero offset constant was 0.00005 the gain calibration
constant is 5000/2.49875 = 2001.00.
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.
7.13.13 Calibrate Input Group B
Repeat steps in Paragraphs 7.13.4 – 7.13.12 for input Group B (Inputs 5 – 8).
7.13.14 Analog Output Calibration and Test (Model 218s Only)
The Model 218S has two analog outputs which require calibration. Zero offset and gain are adjusted
for each input via pots on the Model 218 main board.
NOTE:
Analog output calibration must be performed on both analog outputs.
7.13.14.1 Analog Output Zero Adjust
PURPOSE:
To adjust the zero offset error of the analog output amplifier to 0 V.
CONFIG:
The positive lead of the DVM is connected to the analog output positive terminal,
the negative lead is connected to the analog output negative terminal. The DVM
should be set to read DC VOLTS. Via the front panel manually set the analog
output to 0 V.
TOLERANCE: ±2.5 mV
PROCESS:
Adjust the offset adjust pot of the analog output being calibrated until the DVM
displays 0.000 ±0.002 V.
7.13.14.2 Analog Output Gain Adjust
PURPOSE:
To adjust the full scale gain error of the analog output amplifier.
CONFIG:
The positive lead of the DVM is connected to the analog output positive terminal,
the negative lead is connected to the analog output negative terminal. The DVM
should be set to read DC VOLTS. Via the front panel manually set the analog
output to +10 V.
TOLERANCE: ±2.5 mV
PROCESS:
Adjust the gain adjust pot of the analog output being calibrated until the DVM
displays 10.000 ±0.002 V.
7.13.14.3 Analog Output Negative Full Scale Test
PURPOSE:
To check the -10 V output of the Analog Outputs
CONFIG:
The positive lead of the DVM is connected to the analog output positive terminal,
the negative lead is connected to the analog output negative terminal. The DVM
should be set to read DC VOLTS. Via the front panel manually set the analog
output to -10 V.
TOLERANCE: ±2.5 mV
PROCESS:
Check the DVM reading and verify it displays –10.000 ±0.003 V.
