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hewlett-pa: 500A; Electronic Frequency Meter

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » hewlett-pa: 500A; Electronic Frequency Meter
Pius Steiner
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24.Sep.12 09:50

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"From HP Catalog 18A" Laboratory Instruments", Copyrighted 1945."


Wide frequency range
Good sensitivity
Accuracy independent of line voltage changes and tube characteristics
Ten convenient scale ranges

Beat frequency between two RF signals
Crystal frequency deviation
Audio frequencies
Speed of rotating machinery
Oscillator stability


The -hp- Model 500A directly measures the frequency of an alternating voltage from 5 cps to 50 kc. It is suitable for laboratory and production measurements of audio and supersonic frequencies.
The frequency meter consists of a wide band amplifier with a limiting circuit, and electronic switch, a constant current supply, a frequency discriminating circuit, and an output meter and rectifier. The input signal is amplified and used to switch the constant current source to alternate load resistors. The voltage developed across these resistors is applied to a condenser, and the output meter indicates the average value of the rectified charging current. (See diagram above.) The circuit is designed so that each pulse of charging current has the same average value, making the meter reading proportional to the number of pulses per second, and hence proportional to the frequency of the input signal.


The reading is practically independent of the input voltage waveform, as normal waveform errors cannot affect the electronic switching operation. The regulated current source makes the reading independent of variations in input signal voltage, line voltage, and vacuum tube characteristics. A multiplier switch in the meter circuit provides ten convenient scale ranges. Provision is made for checking the calibration against power line frequency.


The -hp- 500A will measure directly and without any precautions the frequency of any source in the audio and supersonic range. In frequency measurement work at higher frequencies, with the aid of a detector it can be used to measure the frequency difference between two radio frequency signals. It is particularly suited to crystal grinding work, where it can be used to measure the frequency deviation from the standard quickly and accurately. Similarly it may be used to measure oscillator and transmitter frequency stability. With the aid of a magnetic pickup it may be used to measure speed of machinery and rate of vibration. Provision is made to operate an Esterline-Angus 1 ma. recorder with the Model 500A for a continuous record of frequency.


Frequency Range: 5 cycles to 50 kc, in ten ranges having full scale values of 50, 100, 200, and 500 cycles, and 1, 2, 5, 10, 20, and 50 kc.

Input: An input voltage of at least 0.5 volts is required and the input impedance is 50,000 ohms. Variation of the input voltage from 0.5 volts to 200 volts will affect the reading of the meter by not more than plus or minus 1%.

Accuracy: The overall accuracy of the meter is plus or minus 2% of full scale value. A line voltage variation of from 105 volts to 125 volts will affect the meter reading by not more than plus or minus 1%.

Recorder Output: Jack provided on right-hand side of panel for use with 1 milliampere, 1400 ohm Esterline-Angus Automatic Recorder.

Power Supply: 115 volts, 50/60 cycles, 65 watts.

Mounting: The instrument is available in either cabinet or relay rack mounting. The panel size is 8 ¾" x 19" and the depth is 12".

Weight: Net weight, 28 pounds; shipping weight, 44 pounds.



The Electronic Tachometer, new -hp- Model 505A and 505B, is a natural development from the 500A Electronic Frequency Meter. By connecting a photocell pickup in combination with a light source to this basic instrument, it becomes an electronic tachometer, capable of counting speeds or revolutions over a wide range, from about 300 rpm (5 cps) to 3,000,000 rpm (50,000 cps). The light illuminates the moving part to be measured, which is prepared with alternate reflecting and absorbing surfaces. The interrupted reflected light is picked up by the photocell; the electrical impulses generated thereby are transmitted to the frequency meter. The-hp- Electronic Tachometer is capable of measuring very high speeds of moving parts which have small energy or which for other mechanical reasons cannot be mechanically connected to any measuring device. The danger of fractional or multiple errors, inherent in other measuring methods, is eliminated.


The Electronic Tachometer consists of a photo cell and a light source mounted on a stand and an electronic frequency counter which is similar to the -hp- Model 500A. Two tachometer models are supplied. The -hp- Model 505A is calibrated in rpm and the -hp- Model 505B is calibrated in rps.

Speed Range: Model 505A: 300 rpm to 3,000,000 rpm full scale reading, in ten ranges. Model 505B: 50 rps to 50,000 rps full scale reading in ten ranges.

Circuit and Construction: Similar to -hp- Model 500A except for calibration.

Photo Coll: Type 924 phototube. Mounted in shielded tube same size as light source and provided with condensing lens to focus reflected light on phototube. Three-foot cable connects photocell to frequency meter.

Light Source: 15 candle power, 6 volt automotive bulb, mounted in shielded tube. Condensing lens concentrates light.

Net weight 38 pounds, shipping weight 50 pounds.


This article was edited 25.Sep.12 12:11 by Pius Steiner .