Sect. IV Page 2 Model 803A
is calibrated to indcate the ratio o the balanced those shown in the Short Circuit Impedance Chart
voltages in terms of impedance. below. When each frequency is set, balance
the bridge and note the reading. These readings
Thephase angle of the impedance under test is de- should agree within 1% of the tabulated readings
termined by the angle between E andEe The null, shown in the table. For proper short circuit
found at the cancellation point of tkse two voltages, readings the shorting plug, supplied with the in-
is detected by a probe sliding around a circular strument, must be adjusted so that the red dot
slotted section represented on the schematic as a is at the top.
loop. With a pure resistive load the current and
voltage in the system will be in phase, but E and
Ee will be out of phase, and when the pis-up CAUTION
probes are balanced the null will occur at the
THERE IS NO REASON FOR REMOVINGTHE REAR
center of the slotted section with a dial indication COVER OF THE INSTRUMENT.
of zero degrees phase angle.
With a reactive load the current and voltage in the
system will not be in phase, and the null will be Experience has shown that many bridges are dam-
displaced to one side or the other of center in aged by removing the rear cover, .particularly
the slotted section. The amount and direction of if the PHASE dial is not set to 45' before re-
displacement will depend upon the phase angle moving the cover.
and nature of the reactive load.
4-3 MAINTENANCE GENERAL
4-2 ACCURACY CHECK The overall calibration of the instrument is in
part maintained by the setting of the various
The accuracy of the Model 803A may bechecked by drive set screws. These screws should not be
connecting the shorting plug supplied with the
instrument to the UNKNOWN terminal and ac- adjusted. If the accuracy check reveals that the
curately setting the frequency of operation to instrument is out of calibration, consult your field
sales engineer or write directly to the factory
explaining the nature of the problem.
SHORT CIRCUlT IMPEDANCE CHART
For Serial 4-4 LUBRICATION
The FRONT cover should be removed to lubricate
Freq. Freq. MC MC the gears and attenuator pistons. DO NOT REMOVE
THE REAR COVER. Lubrication once a year
should be adequate.
100 100 A dry graphite or molybdenum disulfide powder
is a preferred lubricant for the attenuator pistons.
I 200 Apply sparingly with a small artist's brush.
I 300 The gears may be lubricated with a light moly
grease, available from Hewlett-Packard under
400 Stock NO. 850-137.
500
DO NOT OVER LUBRICATE. |