HEWLETT PACKARD (HP) 803A
Manual de Servicio

Sect. IV Page 2
is calibrated to indcate the ratio o the balanced voltages in terms of impedance.

Model 803A those shown in the Short Circuit Impedance Chart below. When each frequency is set, balance the bridge and note the reading. These readings should agree within 1% of the tabulated readings shown in the table. F o r proper short circuit readings the shorting plug, supplied with the instrument, must be adjusted so that the red dot is a t the top. CAUTION THERE IS NO REASON FOR REMOVINGTHE REAR COVER OF THE INSTRUMENT.

Thephase angle of the impedance under test is determined by the angle between E andEe The null, found at the cancellation point of t k s e two voltages, is detected by a probe sliding around a circular slotted section represented on the schematic as a loop. With a pure resistive load the current and voltage in the system will be in phase, but E and E e will be out of phase, and when the p i s - u p probes are balanced the null will occur at the center of the slotted section with a dial indication 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 displaced to one side or the other of center in the slotted section. The amount and direction of displacement will depend upon the phase angle and nature of the reactive load.

Experience has shown that many bridges a r e damaged by removing the rear cover, .particularly if the PHASE dial is not set to 45' before removing the cover.
4-3 M A I N T E N A N C E GENERAL

4-2

ACCURACY CHECK

The accuracy of the Model 803A may bechecked by connecting the shorting plug supplied with the instrument to the UNKNOWN terminal and accurately setting the frequency of operation to SHORT CIRCUlT IMPEDANCE CHART F o r Serial

The overall calibration of the instrument is in part maintained by the setting of the various drive set screws. These screws should not be adjusted. If the accuracy check reveals that the instrument is out of calibration, consult your field sales engineer o r write directly to the factory explaining the nature of the problem.
4-4
LUBRICATION

Freq. MC

The FRONT cover should be removed to lubricate the gears and attenuator pistons. DO NOT REMOVE THE REAR COVER. Lubrication once a year should be adequate. A dry graphite or molybdenum disulfide powder is a preferred lubricant for the attenuator pistons. Apply sparingly with a small artist's brush. The gears may be lubricated with a light moly grease, available from Hewlett-Packard under Stock NO. 850-137.

100

I I

200
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500

DO NOT OVER LUBRICATE.