Lake Shore 234, User Manual

Page: 38 / 49

Lake Shore Model 234/234D User’s Manual
5-6 Service
The table below indicates the serial command or Range Switch used in
calibration. When the transmitter is calibrated with the Serial Computer Port,
use the serial command shown in the table. When the Calibration Switch
S2
is used, then the Range Switch shown must be selected.
Internal
Serial Range Calibration Reference
Command Switch Resistance Resistor(s)
CAL0 1 1
Ω
10
Ω
CAL1 2 10
Ω
100
Ω
CAL2 3 100
Ω
1 k
Ω
CAL3 4 1 k
Ω
3.16 k
Ω
10 k
Ω
CAL4 5 10 k
Ω
31.6 k
Ω
100 k
Ω
CAL5 6 100 k
Ω
316 k
Ω
5.4.1 Required Equipment for Calibration
1. A digital voltmeter (DVM) that measures DC voltage of 10 mV and 10
volts accurately to 0.005%.
2. A regulated 5 VDC power supply with tolerance within ±0.25V, capable of
sourcing 500 mA on an S-760 or S-765 Switchcraft or equivalent power
plug (0.218 inch outside diameter, accepts 0.08 inch diameter pin). The
positive 5V is on the sleeve, the return in the center pin.
3. The mating screw terminal to the Model 234 front panel signal connector.
4. 1
Ω
, 10
Ω
, 100
Ω
, 1 k
Ω
, 10 k
Ω
, and 100 k
Ω
0.01% resistors to simulate
the sensor for calibration.
5. A 500
Ω
, 0.02%, 1 – 3W resistor to load the 4-20 mA output.
5.4.2 Preparation and General Test
1. Function of the I/V switch. Position I (switch 8 open) of the I/V switch
is normal operation with the output 4 to 20 mA. In position V (switch 8
closed), the output current is between 0 and 20 mA.
2. Function of the T/R Switch. Normal operation is with the T/R in the T
position (switch 7 open) where a CalCurve option is chosen to produce
an output in temperature. With the switch in the
R position the output
current is proportional to the logarithm (base 10) of the resistance of the
sensor. In the
R position, the I/V switch selects either 4 to 20 mA or 0 to
20 mA. In the V position the output is between 0 and 20 mA with 0 mA for
log(R) =0 and 20 mA for log(R) = 6. With the I/V switch in the I position
the output is between 4 and 20 mA with 4 mA for log(R) =0 and 20 mA
for log(R) = 6.