General Radio 546-C Audio Frequency Microvolter Instruction Manual

General Radio 546-C Audio Frequency Microvolter

Product Information

Audio-Frequency Microvolter

Specifications

• Output Voltage Range: 0.5 fl-V to 1.0 v, with 2.2-v input voltage
• Accuracy: For open-circuit output voltages, the calibration is accurate up to 100,000 cps
• Output Impedance: Approximately 600 ohms
• Input Impedance: Refer to paragraph 3.3
• Waveform Error: Refer to paragraph 3.4
• Temperature Error: Refer to paragraph 3.5
• Power Source: The driving oscillator must be able to supply about 2.2v across 600 ohms, or about 8 mw
• Terminals: Jack-top binding posts with standard 3/4-in. spacing
• Dimensions: Width 10, height 7-1/8, depth 6-1/8 inches (255 by 180 by 155 mm), overall
• Net Weight: 6-1/2 lb (3 kg)

Product Usage Instructions

Section 1: Introduction

Purpose:
The purpose of this product is to provide accurate measurements of audio- frequency voltages.

Description:
The Audio-Frequency Microvolter is a device manufactured by General Radio Company. It is designed to measure and output audio-frequency voltages within a specified range. It has various terminals and settings that allow for precise measurements.

Oscillator Requirements:
The driving oscillator used with the Audio-Frequency Microvolter must be capable of supplying approximately 2.2v across 600 ohms or about 8 mw of power.

Section 2: Operating Procedure

Normal Operation:
To use the Audio-Frequency Microvolter in normal operation, follow these steps:

1. Connect the driving oscillator to the Microvolter’s terminals using the provided jack-top binding posts.
2. Set the desired input voltage within the range of 0.5 fl-V to 1.0 v.
3. Adjust the output setting as needed, keeping in mind that the output impedance is approximately 600 ohms.
4. Read the output voltage on the Microvolter’s display or connected measuring device.

Use of Input Voltages Less Than 2.2 Volts:
If you need to use input voltages less than 2.2 volts, refer to paragraph 3.3 in the user manual for instructions on adjusting the input impedance.

D-C Voltages:
The Audio-Frequency Microvolter is not designed to measure direct current (D-C) voltages. It is specifically for audio-frequency measurements.

Measurement of Unknown Voltages:

To measure unknown voltages using the Audio-Frequency Microvolter, follow these steps:

1. Connect the driving oscillator to the Microvolter’s terminals.
2. Set the input voltage to a known value within the specified range.
3. Measure the output voltage and record the reading.
4. Disconnect the driving oscillator and connect the unknown voltage source to the Microvolter’s terminals.
5. Adjust the output setting if necessary and measure the output voltage.
6. Compare the measured output voltage to the recorded value from the known input voltage to determine the unknown voltage.

Section 3: Errors and Corrections

Temperature Error:
Refer to paragraph 3.3 in the user manual for information on temperature errors and any necessary corrections when using the Audio-Frequency Microvolter.

Waveform Error:
Refer to paragraph 3.4 in the user manual for information on waveform errors and any necessary corrections when using the Audio-Frequency Microvolter.

Output Impedance:
The output impedance of the Audio-Frequency Microvolter is approximately 600 ohms. Refer to paragraph 3.5 in the user manual for more details on output impedance and its implications.

Section 4: Service and Maintenance

General:
If you require service or maintenance for the Audio-Frequency Microvolter, please contact one of the General Radio Company Service Departments listed in the user manual.

Potentiometer Electrical Noise:
For information on potentiometer electrical noise and any necessary corrections, refer to paragraph 4.2 in the user manual.

FAQ (Frequently Asked Questions)

Q: Can I use input voltages higher than 2.2 volts with the Audio- Frequency Microvolter?
A: No, the recommended input voltage range for the Audio-Frequency Microvolter is 0.5 fl-V to 1.0 v with a maximum input voltage of 2.2 volts.

Q: Can the Audio-Frequency Microvolter measure direct current (D-C) voltages?
A: No, the Audio-Frequency Microvolter is specifically designedfor measuring audio-frequency voltages and is not suitable for measuring direct current.

Q: How can I calibrate the Audio-Frequency Microvolter?
A: The calibration of the Audio-Frequency Microvolter is done automatically for open-circuit output voltages. For more information on calibration procedures, refer to the user manual.

SPECIFICATIONS

• Output Voltage Range:
  0.5 fl-V to 1.0 v, with 2.2-v input voltage.

• Accuracy:
  For open-circuit output voltages the calibration is accurate within ±(3% + 0.5 fLY) for output settings above 1 f-1-V and for all frequencies between 20 and 20,000 cps.
  For frequencies up to 100 kc the calibration is accurate within ±5% for output settings above 100 JLV. These specifications apply only where waveform and temperature errors are negligible (see below).
  In calculating ratios of output voltages at a given frequency, the accuracy of any given reading can be considered to be within ±(2% + 0.5 JLV), at frequencies up to 100,000 cps. At frequencies above 20 kc this accuracy applies only at levels above 100 JLV.

• Output Impedance:
  Approximately 600 ohms and is constant with setting within ±5%. This impedance is low enough so that no correction on output voltage is necessary for load impedances of the order of 100,000 ohms or more.

• Input Impedance:
  Approximately 600 ohms, substantially independent of output setting on all but the highest multiplier setting.

• Waveform Error:
  Refer to paragraph 3.4.

• Temperature Error:
  Refer to paragraph 3.3.

• Power Source:
  The driving oscillator must be able to supply about 2.2v across 600 ohms, or about 8 mw.

• Terminals:
  Jack-top binding posts with standard 3/ 4-in. spac ing.

• Dimensions:
  Width 10, height 7- l/8, depth 6- l/8 inches (255 by 180 by 155 mm), over-all.

• Net Weight:
  6- l/2 lb (3 kg).

INTRODUCTION

PURPOSE. The Type 546-C Audio-Frequency Microvolter (Figure I) is a calibrated attenuator or voltage divider which, when used with a suitable oscillator, supplies small, accurately known audio-frequency voltages.
Use of the Microvolter converts an oscillator into a standard-signal generator, valuable in such measurements as gain or loss, frequencyresponse characteristics, overload level, and hum level on amplifiers,
networks, and other audio-frequency equipment. The combination of oscillator and Microvolter is also useful in the measurement of the generated voltage of microphones, vibration and phonograph pickups, and other transducers by the insert-voltage method. The Microvolter provides the standardizing voltmeter and the calibrated attenuator necessary to supply accurately known voltages from 0.5 microvolt to I volt(open circuit).

DESCRIPTION.

1. GENERAL. The Microvolter consists, essentially, of a constantimpedance attenuator and a voltmeter by which the input to the attenuator is standardized. A switch controls the output voltage in decade steps, while an individually calibrated dial provides continuous control over each decade.

2. CONTROLS. The only controls are the OUTPUT and MULTIPLIER
   dial-knobs, by means of which the output voltage is set. The OUTPUT control is a continuous rotary knob and dial, the latter calibrated in voltage and in decibels above I microvolt. The voltage scale is approximately logarithmic, aad the decibel scale approximately linear. The MUL TIPLIER control is a six- position rotary switch, whose dial is calibrated in decade steps from I microvolt to 100 millivolts. The MULTIPLIER dial is also calibrated in 20-db steps from 0 to IOO db.
   A meter on the front panel indicates input in volts and in decibels.

3. CONNECTIONS. A pair of jack-top binding posts, marked INPUT, provide the connection between the source of audio-frequencyvoltage and the Microvolter. Another pair of similar binding posts, marked OUTPUT, are the terminals at which the voltage indicated on the dials is available.

GENERAL RADIO COMPANY

OSCILLATOR REQUIREMENTS. Anaudio-frequency oscillator must be used to furnish voltage to the Microvolter. Oscillator output requirements are about 2.2 volts across 600 ohms, or about 8 milliwatts. The following General Radio oscillators are suitable:

• Type 1210-C Unit R-C Oscillator
• Type 1214-A Unit Oscillator
• Type 1301-A Low-Distortion Oscillator
• Type 1304-B Beat-Frequency Audio Generator
• Type 1307 -A Transistor Oscillator

OPERATING PROCEDURE

NORMAL OPERATION. To provide an audio-frequency output between 0.5 microvolt and 1 volt, proceed as follows:

• Connect a suitable audio-frequency oscillator (refer to paragraph 1.3) to the INPUT terminals of the Microvolter.

• Connect the INPUT terminal marked G to the low-potential side of the oscillator, and, if possible, ground this connection.

• Vary the output of the oscillator until the Microvolter meter indicates 2.2 volts (0 db).

• Set the OUTPUT and MULTIPLIER dials so that the product of their voltage settings equals the desired output voltage. For highest accuracy, use the portion of the OUTPUT dial between 1.0 and 10. For example, if the desired output voltage is 50 microvolts, set the OUTPUT dial to 5 and the MULTIPLIER dial to 10 MICROVOLTS. If the desired output is 70 millivolts_, set the OUTPUT dial to 7 and the MULTIPLIER dial to 10 MILLIVOLTS. Output in terms of decibels above 1 microvolt is denoted by the algebraic sum of the decibel indications on the two dials. Since the reference level is 1 microvolt, almost all decibel readings will be positive throughout the range of the instrument. When the Microvolter is used to supply a 600-ohrn load, the output dbm (decibels above 1 milliwatt) equals the output in decibels above 1 microvolt minus 123.8 db.

• For all ordinary measurement purposes the OUTPUT terminals can be considered the terminals of a 600-ohrn generator having the opencircuit terminal voltage indicated by the dial settings.
  CAUTION
  Never connect the Microvolter OUTPUT terminals across a circuit carrying current, either ac or de. If the voltage drop at the OUTPUT terminals is over 4 volts, the Microvolter may be permanently damaged, while smaller drops may cause erroneous voltmeter indications.
  TYPE 546-C AUDIO-FREQUENCY MICROVOLTER

• If the output voltage is lOOmicrovolts or less, use a shielded oscillator and cup-shielded leads.

USE OF INPUT VOLTAGES LESS THAN 2.2 VOLTS.
Since all dial markings are based on an input of2.2 volts, an input of less than 2.2 volts would produce output voltages less than their indicated values. For instance,if the source is able to supply only 1.1 volts, the output voltage is one-halfthat indicated on the dials. This simple relationship is expressed:

Also, if reduced power input is unavoidable, the meter indication in decibels can be added algebraically to the dial decibel indications.
Although it might seem that the useful output range of the Microvolter is increased by the above methods, any such increase is achieved at the expense of accuracy.

D-C VOLTAGES. The Microvolter can be used on direct current if an external meter is used to measure the input voltage.

MEASUREMENT OF UNKNOWN VOLTAGES

1. GENERAL. TheMicrovolter can be used to measureunknown voltages either directly by means of the Microvolter or by substitution methods.
   Voltmeter errors (refer to Section 3) must be considered when the Microvolter meter is used to indicate directly voltage applied to the INPUT terminals.

2. SUBSTITUTION METHOD. In the substitution method, an unknown voltage can be fed into an external, high -impedance meter, and the deflection noted. With the input to the Microvolter at 2.2 volts, the Microvolter output can be fed into the same meter, and the dials adjusted to produce the same deflection. The Microvolter dial settings will then indicate the unknown voltage. If necessary, connect a resistor in series with the external meter to produce a high input impedance.

3. INSERT-VOLTAGE METHOD. Several measurement techniques using the insert-voltage method can be devised, but the following example will serve to demonstrate the principles involved. Connect the source of the voltage to be measured, the Microvolter, an amplifier, and an external meter as shown in Figure 2. Set the Microvolter dial to zero and supply the unknown voltage to the external meter, noting the deflection. Then,with the unknown remaining in circuit but not supplying any voltage, vary the Microvolter dials to produce the same deflection on the external meter as noted before. (The Microvolter should be operating with an input of 2.2 volts.) With the impedance values shown in the diagram, the unl.cnown voltage will be or 1/100 of that indicated on the Micro-volter dials, since this gives the equivalent open -circuit voltage from the Microvolter across Y-Y in the diagram. The voltage measured is the equivalent open -circuit voltage across X-X in the diagram.
   For the circuit arrangement shown in Figure 2, it is essential that the unknown be operated ungrounded, so that the 10-ohm calibration resistor is not shorted by multiple grounds. Any stray capacitance to ground should be kept sufficiently low so that the shunting effect on the 10-ohm resistor is negligible.

ERRORS AND CORRECTIONS

1. GENERAL. The Microvolter is designed for use without calibration charts or correction curves, and its accuracy is more than sufficient for most measurements. Where extremely high accuracy is required or where the limits of error must be known, the following information should prove helpful.

2. OVER-ALL ACCURACY. For output settings above 1 microvolt at frequencies from 20 to 20,000 cps, the open-circuit output-voltage calibration is accurate to within ±(3% + 0. 5 microvolt). At frequencies up to 100 kc the calibration is accurate to within ±5% for output settings above 100 microvolts. These specifications apply only when wavefonn and ternperature errors are negligible (refer to paragraphs 3.3 and 3.4).
   In calculating ratios of output voltages at a given frequency, the accuracy of any given reading can be considered to be within ± ( 2% + 0.5 microvolt), at frequencies up to 100 kc. At frequencies above 20 kc this accuracy applies only at output levels above 100 microvolts.
   To reduce errors in absolute-voltage values, check the Microvolter against an accurate vacuum -tube voltmeter, such as the General Radio
   Type 1800-B. Set the Microvolter for an output of 1000 millivolts, and adjust the input voltage to the Microvolter until the vacuum -tube voltmeter indicates 1 volt. Thus, if the input to the Microvolter is maintained, output voltages will be as indicated on the Microvolter dials. This check can be repeated for different frequencies and operating temperatures.

3. TEMPERATURE ERROR. Any initial error that may be present in the indicating meter has been compensated for by calibration of the OUTPUT dial. As with all copper-oxide instruments, the meter is somewhat affected by temperature variations. Calibration is correct at 77 degrees F. For room temperatures below this value the correction is -0.0046 vo~t per degree F. For temperatures above 77 degrees F, the correction is +0.0023 volt per degree F. These corr·ections should be applied to the normal2.2 -volt meter indication to obtain the correct indication at the operating temperature. For example, if the temperature is 97 degrees F, the correction is +0.0023 (97 -77), or 0.046volt. This correction, added to the standard meter indication of 2.2 volts, gives a corrected meter setting of 2 .246 volts. The accuracy of the calibration. is independent of temperature when the Microvolter is used as an attenuator or voltage diviqer.

4. WAVEFORM ERROR. The accuracy of the Microvolter as a calibrated attenuator or voltage divider is independent of waveform. However, the absolute accuracy of the output voltage calibration depends on the characteristics of the input copper-oxide rectifier voltmeter, which has a waveform error that depends in turn on both the phase and the magnitude of hannonics present in the input. If the input voltage is not a pure sine wave, the resultant error for absolute measurements can be nearly as great as the percentage of harmonics present. This error can usually be overlooked when the Microvolter is used with ordinary laboratory oscillators.
   The rectifier-type voltmeter itself introduces some distortion unless the source impedance is very low. With a source impedance of 600 ohms the distortion introduced is about 0.2 percent.

5. OUTPUT IMPEDANCE. Since the Microvolter indicates open-circuit voltages, the internal output impedance must be taken into account with low-impedance loads. For loads greater than 100,000 ohms no correction need be made.

SERVICE AND MAINTENANCE

1. GENERAL. The two-year warranty given with every General Radio instrument attests the quality of materials and workmanship in our products.
   When difficulties do occur, our service engineers will assist in any way possible.
   In case of difficulties that cannot be eliminated by the use of these service instructions, please write or phone our Service Department, giving full information of the trouble and of steps taken to remedy it. Be sure to mention the serial and type numbers of the instrument.
   Before returning an instrument to General Radio for service, please write to our Service Department or nearest district office (see back cover), requesting a Returned Material Tag. Use of this tag will insure proper handlingand identification. For instruments not covered by thewarranty, a purchase order should be forwarded to avoid unnecessary delay.

2. POTENTIOMETER ELECTRICAL NOISE. Occasionally, rotation of the OUTPUT control may cause some electrical noise. This condition can be alleviated if the control is rapidly swept back and forth a few times.

PARTS LIST:

REF

DESIG

| DESCRIPTION| GR PART NO.
---|---|---
ClA ClB Ml Rl R2 R3 R4 RS R6 R7 RB R9

RlO Rll Rl2 Rl3 Rl4 RlS Rl6 Rl7 Sl

| CAPACITOR, Trimmer, 10-lOOµµf, 500 dcwv CAPACITOR, Mica, lOOµµf ±loX,

METER

RESISTOR, 4000  ±0.25%     l

RESISTOR, 4 k  ±0.25%

RESISTOR, 4000  ±0.25%

RESISTOR, 44.440  ±0.25% }

RESISTOR, 3560  ±0.25%

RESISTOR,  420-4400             }

RESISTOR, 2000  ±5%

RESISTOR, 18000  ±0.25%

RESISTOR, 1780  ±0.25%    }

RESISTOR, 22.20  ±0.5%

RESISTOR, 1780  0.25%

RESISTOR, 18000  ±0.25%  }

RESISTOR, 2000  ±0.25%

RESISTOR, Film, 4170  ±1/2%, l/2w

RESISTOR, Wire-wound, 3900 ±5%, l/2w

RESISTOR, Wire-wound, 150 ±10%, 1/2 w RESISTOR, Composition, 12 k ±10%, 1/2 w SWITCH

| COT-24 COM-20B MEDS-115

546-302

546-303

546-30

546-304

546-305

REF-70 REW-3C REW-3C

REC-20BF 546-321

Read User Manual Online (PDF format)

Read User Manual Online (PDF format)  >>

Download This Manual (PDF format)

Download this manual  >>