Section 3
OM6634A-B-02
4 January 2019
3-1
3. OPERATING INSTRUCTIONS
3.1.
INSTALLATION
The model 6634A has been shipped with the line input voltage set to 240 volts with the fuse
removed unless specifically requested to be set to another voltage level. The line input selectors
must be set to the correct line voltage before power is applied to the instrument. Remove the
warning label positioned across the power cord only after checking the setting of the operating
voltage. The line input voltage selection must be set correctly. The settings available are 100 V,
120 V, 220 V, and 240 V. Figure 3-1 details the line input voltage selector setting.
The instrument is supplied with a North American style line cord, unless otherwise specified at
time of order. Ensure that the line cord is plugged into a wall socket or extension cord that has a
protective or safety ground. Where 3-contact power supply outputs are not available, a suitable
protective ground connection must be made before switching the instrument power on. Any
interruption of the protective ground may possibly render the instrument unsafe.
To set the correct line input voltage pry open the power receptacle on the rear panel as shown in
Figure 3-1.
Place the instrument on a vibration-free bench or install it in an equipment rack as required.
Connect the line cord to the appropriate line power outlet and switch the instrument on using the
power switch at the back of the instrument at the line input connect.
The red POWER lamp should light, together with the green HEATER lamp.
When the inner chamber containing the standard resistors reaches its operating temperature, the
HEATER lamp will indicate periodic cycling. Due to the thermal lagging, it will take several
hours to raise the inner chamber and the standard resistors to the operating temperature. The
standard resistors should be allowed to stabilize at the operating temperature for at least 36 hours
before measurement or use.
3.2.
OPERATING NOTES
3.2.1.
Connection to Standard Resistors
Connection to the resistor terminals should be made with solid copper wire having low
thermal EMF characteristics. The wires to each C-P pair of standard resistor terminals
should be twisted and preferably shielded to avoid spurious pick-up. Use Guildline Type
SCW Wire or equivalent. The certified resistance of each resistance element installed
and the date of calibration are indicated in the Report of Calibration.
3.2.2.
Monitoring of the Internal Temperature
The PRT which comes to the front panel is used to measure the internal temperature.
Connect an ohmmeter capable of four wire resistance measurement with low excitation
current. Connect the current leads to C1 and C2, and the respective potential leads to P1
Summary of Contents for 6634A Resistance Standard
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