Maintenance; Line Voltage Selection; Calibration; Current Source Calibration - Lakeshore 818 User Manual

5.1 CHECKING OR REPLACING FUSE
CAUTION: To prevent shock hazard, turn off instrument and disconnect it from AC line power and all
test equipment before replacing fuse.
1. Set POWER switch to OFF and disconnect power cord from unit.
2. The fuse compartment is located to the right of the power connector. Carefully pry open the fuse
compartment cover with a small screw driver.
3. Remove the upper fuse holder by sliding it out of its position with the screw driver.
CAUTION: For continued protection against fire hazard, replace only with fuse of same type and rating
specified for the line voltage selected.
4. For the Model 818, replace the fuse with 0.25 A for 110 VAC operation, or 0.125 A for 230 VAC operation.
For the Model 819, replace the fuse with 0.5 A for 110 VAC operation, or 0.25 A for 230 VAC operation.
5. Replace fuse holder, close fuse compartment, and connect the power cord.
5.2

LINE VOLTAGE SELECTION

The rear panel, three-pronged line power connector permits the Model 818/819 to be connected to 115 or
230 VAC line voltages. Use the following procedure to change the line voltage:
CAUTION: To prevent shock hazard, turn off instrument and disconnect it from AC line power and all
test equipment before changing the line voltage.
1. Set POWER switch to OFF and disconnect power cord from unit.
2. The line voltage selection switch is located to the right of the power connector. Use a small screw driver to
slide the switch to the 115 or 230 VAC position.
3. Install the proper fuse as outlined in Section 5.1.
5.4

CALIBRATION

Required equipment:
1. Digital Voltmeter/Multimeter (DVM) - 4½ digit resolution or better.
2. Precision Resistors - 25 kΩ and 125 kΩ with a tolerance of ±0.01% or better.
Warm-up unit for one hour to achieve rated specifications.
5.4.1

Current Source Calibration

1. Configure the 125 kΩ resistor to simulate a sensor in the two-lead configuration shown in Figure 2-1. For
the Model 819, install the 125 kΩ resistor in INPUT 1. Set the Model 819 into scan mode with all dwell
times set to 0, and select channel 1 as the display channel.
2. Connect DVM voltage leads across resistor and adjust the rear panel trimpot marked I ADJ until voltage
across resistor is 1.2500 volts ±100 microvolts.

Maintenance

Lake Shore Model 818 / 819 Cryopump Monitor User's Manual
CHAPTER 5
MAINTENANCE
5-1