RFL 904 Manuale utente

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INSTRUCTIONS

Model 904

GAUSSMETER

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1980

RFL Industries, Inc.

Book MA-48540

CAUTION

FOR YOUR SAFETY

THE INSTALLATION, OPERATION AND

MAINTENANCE OF THIS EQUIPMENT

SHOULD BE PERFORMED BY

QUALIFIED PERSONS ONLY.

WARRANTY

The Models 904 and 904T are warranted

for 12 months from date of delivery for

replacement of any part, except for probes,

which fails during normal operation or ser-

vice. A deficient part should be returned to

the factory, shipping charges prepaid, for

replacement f.o.b. Boonton, N. J.

RFL Industries, Inc.

Boonton, New Jersey 07005

WARNING:

The Equipment Herein Described Contains High Voltage

Exercise due care during operation and servicing.

Read safety summary on reverse of this page.

CONTENTS

Description

Specifications

III

Theory of Measurement

Operating Instructions

Probes

Flat, or Transverse-Field Probes

Axial Probes

Tangential Flat Probes

Maintenance and Calibration

Maintenance

Calibration

VII

Circuit Details

Power Supply

Signal Circuits

Indication

Adjustments

VIII

Parts List

SAFETY SUMMARY

The following safety precautions must be observed at all times

during operation, service, and repair of this product. Failure to

comply wills these precautions, or with specific warnings

elsewhere in this manual violates safety standards of design,

manufacture, and intended use of the product. RFL assumes no

liability for failure to comply with these requirements.

GROUND THE EQUIPMENT

To minimize shock hazard, chassis, cabinets, and equipment

racks must be connected to an electrical ground. AC powered pro-

ducts should be equipped with a three-conductor power cable, or

equivalent connection on a terminal block. Power cables must

either be plugged into an approved three-contact electrical outlet

or used with a three-contact or two-contact adapter with the

grounding wire (green) firmly connected to an electrical ground

(safety ground) at the power outlet. The power jack and mating

plug of power cables provided meet International Electrotechnical

Commission (IEC) safety standards. Equipment provided with ter-

minal blocks, operating from either ac or dc, is provided with ap-

propriate means for connecting an electrical safety ground.

DO NOT OPERATE IN AN EXPLOSIVE ATMOSPHERE

Do not operate the product in the presence of flammable gases

or fumes. Operation of any electrical equipment in such an en-

vironment constitutes a definite safety hazard.

DO NOT OPERATE IN WET OR DAMP AREAS

Do not operate the product in wet or damp areas. Operation of

any electrical equipment in such an environment constitutes a

definite safety hazard.

KEEP AWAY FROM LIVE CIRCUITS

Operating personnel must not remove covers. Replacement of

components and internal adjustments must be made by qualified

maintenance persons. Disconnect power cable when replacing

components. Under certain conditions, dangerous voltages may

exist even with the bower cable removed. To avoid injuries

always disconnect power and discharge circuits by grounding

before touching them.

DO NOT SERVICE OR ADJUST ALONE

Do not attempt internal service or adjustment unless another

person capable of rendering first aid and resuscitation is present.

DO NOT SUBSTITUTE PARTS OR

MODIFY EQUIPMENT

Because of the danger of introducing additional hazards, do not

install substitute parts or perform an unauthorized modification to

the equipment. The product may be returned to RFL for service

and repair to ensure that safety features are maintained.

DANGEROUS

PROCEDURE WARNINGS

Throughout this manual, warnings identify potentially

dangerous procedures. Instructions contained therein must be

followed.

Frontispiece: Model 904 Gaussmeter.

The Model 904T Teslameter is similar in appearance.

Chapter I

DESCRIPTION

The Model 904 is a compact instrument designed for measur-

ing intensity of ac, dc, and permanent-magnet magnetic fields

with flux densities from 1.0 to 30,000 gauss (0.0001 to 3

Tesla). The Model 904 Gaussmeter reads flux density in gauss.

The Model 904T Teslameter reads flux density in Tesla. The two

models are identical in all other respects. DC and permanent-

magnet fields are read directly from a zero-left, analog meter. AC

field measurements require the use of an external ac meter or

oscilloscope connected to a rear-panel jack. The analog signal

available from this jack may also be used as a controlling signal for

automatic or semi-automatic magnetic processing systems, or as

input to a recorder.

Polarity of the dc or permanent-magnet field is indicated by two

LEDS located adjacent to the panel meter. This provides the con-

venience of a zero-center meter with the greater scale length of a

zero-left meter.

The instrument uses Hall—effect sensors. A wide choice of

axial,transverse-field, and tangential probes is available. A simple,

internal means for calibration without using a reference magnet is

included.

Both models operate from either 115- or 230-Vac, 48-63-Hz

power. They are enclosed in an impact-resistant plastic case, the

carrying handle of which serves also as a tilt bail to position the

front panel for easy viewing and control.

A simplified schematic of the circuit, Figure 1, outlines the

operation of the instrument.

A constant-current generator supplies excitation current to the

Hall probe, the signal from which is amplified in a two-stage,

direct-coupled amplifier. Magnitude of the signal is indicated on a

d'Arsonval meter; and sensitivity, or range, of the measurement is

set by selecting fixed values of negative feedback for the

amplifiers with a range switch.

Polarity of the field is sensed with voltage comparators and is

indicated with light-emitting diodes whose illumination cor-

responds to the polarity indicated.

Chapter II

SPECIFICATIONS

Full-scale Ranges

Model 904 Gaussmeter: 0 to 30, 100, 300, 1K, 3K, 10K, and

30K gauss.

Model 9041 Teslameter: 0 to 0.003, 0.001, 0.03, 0.1, 0.3,

1.0, and 3.0 Tesla.

Accuracy

For permanent-magnet, dc, and ac fields from 10 to 400 Hz:

±(3% of range plus error of probe).

For ac fields from 401 to 1000 Hz:

±(5% of range plus error of probe).

Downscale Linearity

± 1%

of range.

Operating Temperature Range

12 to 32°C.

Calibration Method

Built-in electronic circuit calibrated against a 0.2% accurate

magnetic reference standard.

Analog Output

+ 1

volt full-scale for any range.

Range Selection

Pushbuttons

Operating Power

1 5/230 Vac, 48-63 Hz, approx. 3.5 watts

Size

8.25" wide, 9" deep, 2.75" high (209 x 228 x 70 mm).

Weight

3.8 lbs. (1.7 kg).

Figure 1. Simplified schematic of Models 904 and 904T.

CONSTANT-

CURRENT

GENERATOR

ICSB

DS34

RANGE

,,-

RANGE

OFFSET I

OFFSET 2

NULL

ANALOG

OUTPUT

METER •

CAL

FITTER

120

-REF /

-12

1055

+REF /

tiAll

CAL

RIT

CAL

READ

CAL

READ

Chapter

III

THEORY OF MEASUREMENT

THE HALL EFFECT

When electrons move in a conductor perpendicular to a

magnetic field, they are deflected toward one side of the conduc-

tor (left or right depending on the direction of the magnetic field)

in a direction normal to the direction of both the initial electron

flow and the magnetic field. The force deflecting the electrons is

directly proportional to the electron velocity (current) and the

magnetic field intensity. This deflection process continues until

sufficient charge has accumulated at the sides of the conductor to

establish a transverse electric field which opposes further deflec-

tion of charge carriers. The transverse potential difference thus

created is called the Hall voltage and the phenomenon causing it is

known as the Hall effect.

The magnitude of this potential in volts is given by

RIH

where E is the Hall voltage, H is the magnetic flux density in

Oersteds, t is the thickness of the sample in centimeters, and R is

the Hall coefficient in volt-cm/ampere gauss.

Under the conditions shown in Figure 2, terminal B will be

negative with respect to terminal A for metals and semiconduc-

tors in which the current is carried by electrons. Reversing the

field reverses the output polarity. As shown by the equation

above, the width of the strip is not a factor of the output as long

as it is large compared to the thickness. The strip should be twice

as long as it is wide or the output drops off. For thin strips the out-

put is unaffected by the frequency of the field in the audio range.

The Hall voltage is maximum when the plane of the element is

perpendicular to the magnetic field.

Practical materials for Hall elements are films and slabs of

specially refined semiconductors. The sensitivity, temperature

stability and linearity to fields can be varied through wide ranges

by selection of materials. One characteristic can usually be im-

proved at the expense of another.

GAUSS

300 .11t, 3K.101(

30K READ-a.

•

(CA1)

-!-(CAL)-a-

At.

VOLTAGE-5

Hz . FUSE

=1 • 115V-125V • •

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- 1/4A

11:3 210V-230V

1/8A

•

- •

RFL' EndusErles,'Enc., Boonton,' New Jersey, as

.A.

• •!

The output voltage from a gaussmeter probe is proportional to

the excitation current, and if this current is held constant then the

Hall voltage will be solely proportional to the incident magnetic

flux, although the precise Hall voltage for constant flux may vary

slightly from one probe to the next. Probes supplied for use with

the Model 904 are standardized at the factory, for use with this

instrument, by marking them with a number which compensates

for this variation. Then, the instrument is calibrated by varing the

magnitude of the constant-current excitation until the meter reads

the number stamped on the probe.

Figure 2. The Hall effect.

Chapter IV

OPERATING INSTRUCTIONS

CAUTION

Be sure that the gaussmeter is unplugged from

the powerline before setting S2, the line-voltage

switch, or before opening the case and changing

Fuse Fl.

INSTALLATION

Determine whether the instrument is to be operated from

1 15-

or 230-volt primary power. The instrument is shipped from the

factory with the voltage-selector switch, S2, Figure 5, set at the

115-volt position, and with a fuse rated for 0.25 ampere at Fl.

For operation from

1 15Vac,

the instrument need only be con-

nected to the power source.

Figure 3. Front and rear panels of Models 904 and 904T.

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For 230-volt operation, the case should be opened, Fl should

be replaced with a fuse rated for 0.125 ampere, and S2 should be

moved to its 230-volt position, after which the instrument may be

powered.

OPERATION

(1)

Connect the Hall probe to its socket on the rear panel. The

location will be seen on Figure 3.

(2)

Set all switches on the front panel, Figure 3, to their out

position. Connect the instrument to its source of power, depress

the POWER switch, and allow the instrument to warm up for ap-

proximately ten minutes before continuing.

(3)

Depress READ/CAL button to CAL.

(4)

Depress 10K/CAL switch to CAL.

(5)

Using the 0-10 scale on the front-panel meter, adjust the

CAL potentiometer so that the meter reads the number which is

stamped on the body of the probe. The instrument is now

calibrated to the characteristics of the individual probe used.

(6)Move CAL/READ button to READ by depressing to release it.

(7)

Depress the 30-gauss (0.003 tesla) range button.

(8)

If a zero-field chamber is available, place the active end of

the probe in the chamber. If no chamber is available, orient the

probe in space so that the earth's magnetic field causes the

minimum deflection on the meter, Then, in either case, adjust the

NULL control for zero on the meter. The instrument is now ready

for use.

It is advisable to recheck the zero condition periodically.

Although under normal conditions it is stable, there is always the

possibility that either the NULL or the CAL control may have been

moved inadvertently.

The tip of the probe is color coded to indicate polarity of the

magnetic field. When the red-marked side of the flat probe, or the

front end of an axial probe is pointed toward a magnetic pole

which attracts the North-seeking end of a compass needle, the

polarity-indicating lamp marked N will be illuminated.

Although every effort has been expended to make the Hall

probe as rugged as possible, it should be remembered that the Hall

element is a fragile component. Use care when handling the

probe. Do not force it into narrow gaps, or apply twisting or bend-

ing forces while the probe is in the confines of a gap. A properly

handled probe will last many years, but carelessness can destroy

the element in a few seconds.

Chapter V

PROBES

The Models 904 and 904T use Hall-effect probes for measuring

flux density. RFL has nine standard Hall-effect probes available for

use with this instrument. Questions on choice and application of

probes and search coils, as well as questions on unusual applica-

tions, may be direct to RFL's Magnetics Engineering Department.

Flat or Transverse-Field Probes

The transverse Hall-probe measures magnetic fields perpen-

dicular to its flat surface. RFL flat probes are supplied in thickness

ranging from 0.015 inch to 0.039 inch. The 0.025 and

0.039-inch probes are enclosed in rugged fiberglass/epoxy

shields to provide maximum protection for the sensitive Hall ele-

ment. All flat probes incorporate a pencil-slim handle and semi-

flexible leads from the element to enable use in a wide variety of

applications. A lightweight, five-foot cable is standard with all flat

probes.

Axial Probe

This configuration is used to measure fields parallel to the probe

handle, such as solenoidal fields. The Hall element is encapsulated

in epoxy and the handle is rigid for several inches beyond the tip.

Various sizes are available. The axial probe, because of its tip con-

struction, is generally less subject to accidental damage than flat

probes. Care must be exercised, however, not to allow the flat

face of the tip to contact abrasive surfaces where any motion is

involved. The Hall element is located only a few thousandths of an

inch behind the face and could be damaged if undue pressure is

placed on it.

Tangential Flat Probe

The tangential probe is similar to the flat probe with the main

difference that the element is placed as close to the edge of the tip

as possible. The flat-probe element is centered between the out-

side edges of its enclosure. This construction puts the element in

close proximity to the outside edges of the enclosure. Care must

be taken, therefore, that the probe will not be subjected to rough

handling.

ACTIVE AREA

.071 X

MIT

ACTIVE AREA

078 X .167

904.200

4 1/4

—I 14-- 5/16

DIA.

..„

ACTIVE AREA

904.312

1561

ts_

.060,1.150

ACTIVE AREA

904.156

.082 0.125

014

11.200—

4—

8-3/4

4,--

ACTIVE AREA

.060

.060 X .150

NOTE:

RFL

reserves the right to change probe dimensions as required.

The tangential probe is used for measuring tangent to the sur-

face of a material where it is necessary to place the probe element

as close to the surface as possible. This enables measurements of

flux densities close to and parallel to a surface where either flux

leakage or anomalies in the material occur.

General

Test-data sheets are supplied with every probe. These contain

electrical and temperature-stability values plus calibration data for

each range of the instrument on which they are used. It is impor-

tant when ordering replacement probes that the model and serial

number of the Gaussmeter be provided. This will assure proper

calibration and assembly of the correct connector.

FLAT PROBES

—011.4--

.020

904.020

—4125/14 R-

1/I9

ACTIVE AREA

.040 0.090

904.015

904.039

-or

-5/32

I-114-- .025

ACTIVE AREA

.076 X .197

904.025

5/32

.039—•1141--

TANGENTIAL PROBE

.040 —4114-

-a

AXIAL PROBES

.030 X .060

—DIA.

DIA.

VI"

8 3/4

904-100

ACTIVE AREA

•

Figure 4. Standard gaussmeter (Hall-effect) probes.

Chapter VI

MAINTENANCE and CALIBRATION

MAINTENANCE

The content of this chapter is primarily a description of pro-

cedures for adjustment of the circuits of the instrument. Failure of

the equipment to perform as required is usually evidence of some

defect in procedure or equipment, and the nature of the failure is

generally a most valuable symptom, when used in conjunction

with the schematic of the circuit, leading to discovery of the

defect. Signal tracing with an oscilloscope is also an effective ap-

proach.

Figure 5 locates the most significant components and ad-

justments.

Figure 5. Location of major controls. Models 904 and 904T.

ACTIVE AREA

.078 X .187

9/32

3/16-

3/8

904-040

11.11•1

•

CALIBRATION

When performing any of the following calibration procedures, it

is recommended that the instrument first be turned on and allow-

ed to warm up for at least ten minutes. With the case removed,

the chassis may be protected from air currents by using a piece of

transparent lucite equipped with a hole for passing the

screwdriver used for adjustments. Then, internal calibration con-

trols are set as follows:

(14)

Plug a standard probe into J1.

(15)

Set the READ/CAL switch to the CAL position by depress-

ing it.

(16)

Depress the 10-K (1-T) range switch.

(17)

Using the 0-10 scale on the meter, adjust CAL control, R19,

on front panel so that the front-panel meter, M1, reads the

number stamped on the body of the probe. The instrument

and probe are now calibrated and ready for use.

(1)

At the socket for the probe, Terminals 1 and 2 must be

shorted together, and Terminals 3 and 4 also must be in-

dependently shorted together. These connections can be

made either by preparing a suitably shorted plug for insertion

in J1, or by clipping leads across the appropriate socket ter-

minals inside the instrument.

(2)

Set all range switches to their OUT position.

(3)

Connect a jumper from TP3 to TP2. This grounds the input

to IC5A.

(4)

Adjust R25, OFFSET 2, for minimum deflection on the front-

panel meter.

(5)

Move the grounding jumper from TP3 to TP1. This grounds

the input of IC4.

(6)

Set NULL on front panel, R8, to center of its range and

depress the 30-gauss (0.003-T) range button.

(7)

Adjust R16, OFFSET 1, for minimum deflection of the meter.

(8)

Remove the jumper at TP3 and the shorting plug or jumpers

used at J2. Then connect a stable, adjustable dc source,

capable of a few tenths of a volt, across J2-1 and J2-2, with

its positive side at J2-1. This serves as an input signal.

(9)

Depress the 30-K (3-T) range button.

(10)

Adjust the dc input voltage until a digital voltmeter, con-

nected to J1, reads precisely 1.00 volt. Then adjust METER

CAL, R30, until M1 reads exactly full scale.

(11)

Observe that the N polarity indicator, DS2, is illuminated

and that DS3 is not.

(12)

Reverse the polarity of the input signal so that J2-1 is

negative. The digital voltmeter should read — 1.00 volt.

Observe that the polarity indicator, DS3, is illuminated and

that DS2 is not.

(13)

The instrument is now calibrated and the combination of in-

strument and probe is now ready for calibration.

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