Omega Products HHG-22 Installation Manual

Model HHG-22

GAUSS / TESLA METER

Instruction Manual

Model HHG-22

GAUSS / TESLA METER

Instruction Manual

This symbol appears on the instrument and probe. It

refers the operator to additional information

contained in this instruction manual, also identified

by the same symbol.

NOTICE:

See Pages 3-1 and 3-2

for SAFETY

instructions prior to first use!

Table of Contents

SECTION-1 INTRODUCTION

Understanding Flux Density.............................................. 1-1

Measurement of Flux Density............................................ 1-2

Product Description........................................................... 1-5

Applications....................................................................... 1-6

SECTION-2 SPECIFICATIONS

Instrument......................................................................... 2-1

Standard Transverse Probe.............................................. 2-3

Standard Axial Probe........................................................ 2-4

Optional Probe Extension Cable....................................... 2-5

Zero Flux Chamber............................................................ 2-6

SECTION-3 OPERATING INSTRUCTIONS

Operator Safety................................................................. 3-1

Operating Features........................................................... 3-3

Instrument Preparation...................................................... 3-5

Power-Up.......................................................................... 3-7

Power-Up Settings............................................................ 3-8

Low Battery Condition....................................................... 3-9

Overrange Condition......................................................... 3-10

AC or DC Measurement Selection..................................... 3-11

UNITS of Measurement Selection..................................... 3-12

RANGE Selection.............................................................. 3-13

HOLD Mode Selection....................................................... 3-15

MIN / MAX Hold Usage...................................................... 3-16

ZERO Function.................................................................. 3-17

Automatic ZERO Function................................................. 3-18

Manual ZERO Function..................................................... 3-20

Sources of Measurement Errors........................................ 3-22

More details on AC Mode Operation................................. 3-25

More details on DC Mode Operation................................. 3-26

WARRANTY....................................................................

4-1

List of Illustrations

Figure 1-1 Flux Lines of a Permanent Magnet............ 1-1

Figure 1-2 Hall Generator............................................ 1-3

Figure 1-3 Hall Probe Configurations.......................... 1-4

Figure 2-1 Standard Transverse Probe....................... 2-3

Figure 2-2 Standard Axial Probe................................. 2-4

Figure 2-3 Optional Probe Extension Cable................ 2-5

Figure 2-4 Zero Flux Chamber.................................... 2-6

Figure 3-1 Auxiliary Power Connector Warnings......... 3-1

Figure 3-2 Probe Electrical Warning........................... 3-2

Figure 3-3 Operating Features.................................... 3-3

Figure 3-4 Battery Installation..................................... 3-5

Figure 3-5 Probe Connection...................................... 3-6

Figure 3-6 Power-Up Display...................................... 3-7

Figure 3-7 Missing Probe Indication............................ 3-8

Figure 3-8 Low Battery Indication................................ 3-10

Figure 3-9 Overrange Indication ................................ 3-10

Figure 3-10 MODE (AC-DC) Function........................... 3-11

Figure 3-11 UNITS Function.......................................... 3-12

Figure 3-12 RANGE Function....................................... 3-14

Figure 3-13 HOLD Function.......................................... 3-16

Figure 3-14 Automatic ZERO Function......................... 3-19

Figure 3-15 Manual ZERO Function.............................. 3-21

Figure 3-16 Probe Output versus Flux Angle................ 3-23

Figure 3-17 Probe Output versus Distance................... 3-23

Figure 3-18 Flux Density Variations in a Magnet........... 3-24

Figure 3-19 Low AC Signal Indication........................... 3-25

Section 1

Introduction

UNDERSTANDING FLUX DENSITY

Magnetic fields surrounding permanent magnets or electrical conductors can be visualized as a collection of magnetic flux lines; lines of force existing in the material that is being subjected to a magnetizing influence. Unlike light, which travels away from its source indefinitely, magnetic flux lines must eventually return to the source. Thus all magnetic sources are said to have two poles. Flux lines are said to emanate from the “north” pole and return to the “south” pole, as depicted in Figure 1-1.

Figure 1-1

Flux Lines of a Permanent Magnet

One line of flux in the CGS measurement system is called a maxwell (M commonly used.

Flux density, also called magnetic induction, is the number of flux lines passing through a given area. It is commonly assigned the symbol “B” in scientific documents. In the CGS system a gauss (G) is one line of flux passing through a 1 cm

), but the weber (Wb), which is 108 lines, is more

area. The more

1-1

INTRODUCTION

commonly used term is the tesla (T), which is 10,000 lines per

. Thus

1 tesla = 10,000 gauss 1 gauss = 0.0001 tesla

Magnetic field strength is a measure of force produced by an electric current or a permanent magnet. It is the ability to induce a magnetic field “B”. It is commonly assigned the symbol “H” in scientific documents. The unit of “H” in the CGS system is an oersted (Oe), but the ampere/meter (A/m) is more commonly used. The relationship is

1 oersted = 79.6 ampere/meter

1 ampere/meter = 0.01256 oersted

It is important to know that magnetic field strength and magnetic flux density are not

the same. The only time the two are considered equal is in free space (air). Only in free space is the following relationship true:

1 G = 1 Oe = 0.0001 T = 79.6 A/m

MEASUREMENT OF FLUX DENSITY

A device commonly used to measure flux density is the Hall generator. A Hall generator is a thin slice of a semiconductor

material to which four leads are attached at the midpoint of each edge, as shown in Figure 1-2.

1-2

INTRODUCTION

Figure 1-2

Hall Generator

A constant current (Ic) is forced through the material. In a zero magnetic field there is no voltage difference between the other two edges. When flux lines pass through the material the path of the current bends closer to one edge, creating a voltage difference known as the Hall voltage (Vh). In an ideal Hall generator there is a linear relationship between the number of flux lines passing through the material (flux density) and the Hall voltage.

The Hall voltage is also a function of the direction in which the flux lines pass through the material, producing a positive voltage in one direction and a negative voltage in the other. If the same number of flux lines pass through the material in either direction, the net result is zero volts. This sensitivity to flux direction makes it possible to measure both static (dc) and alternating (ac) magnetic fields.

The Hall voltage is also a function of the angle at which the flux lines pass through the material. The greatest Hall voltage occurs when the flux lines pass perpendicularly through the material. Otherwise the output is related to the cosine of the difference between 90° and the actual angle.

1-3

INTRODUCTION

The sensitive area of the Hall generator is generally defined as the largest circular area within the actual slice of the material. This active area can range in size from 0.2 mm (0.008”) to 19 mm (0.75”) in diameter. Often the Hall generator assembly is too fragile to use by itself so it is often mounted in a protective tube and terminated with a flexible cable and a connector. This assembly, known as a Hall probe, is generally provided in two configurations:

Figure 1-3

Hall Probe Configurations

In “transverse” probes the Hall generator is mounted in a thin, flat stem whereas in “axial” probes the Hall generator is mounted in a cylindrical stem. The axis of sensitivity is the primary difference, as shown by “B” in Figure 1-3. Generally transverse probes are used to make measurements between two magnetic poles such as those in audio speakers, electric motors and imaging machines. Axial probes are often used to measure the magnetic field along the axis of a coil, solenoid or traveling wave tube. Either probe can be used where there are few physical space limitations, such as in geomagnetic or electromagnetic interference surveys.

1-4

INTRODUCTION

1-5

INTRODUCTION

Handle the Hall probe with care. Do not bend the stem or

apply pressure to the probe tip as damage may result. Use

the protective cover when the probe is not in use.

PRODUCT DESCRIPTION

The MODEL HHG-22 GAUSS / TESLAMETER is a portable instrument that utilizes a Hall probe to measure magnetic flux density in terms of gauss, tesla or ampere/meter. The measurement range is from 0.01 mT (0.1 G or 0.01 kA/m) to

1.999T (19.99 kG or 1591 kA/m). The instrument is capable of measuring static (dc) magnetic fields and alternating (ac) fields.

The MODEL HHG-22 consists of a palm-sized meter and various detachable Hall probes. The meter operates on standard 9 volt alkaline batteries or can be operated with an external ac-to-dc power supply. A retractable bail allows the meter to stand upright on a flat surface. A notch in the bail allows the meter to be wall mounted when bench space is at a premium. The large display is visible at considerable distances. The instrument is easily configured using a single rotary selector and two pushbuttons.

Three measurement ranges can be selected or the meter can automatically select the best range based on the present flux density being measured. A “zero” function allows the user to remove undesirable readings from nearby magnetic fields (including earth’s) or false readings caused by initial electrical offsets in the probe and meter. Included is a “zero flux chamber” which allows the probe to be shielded from external magnetic fields during this operation. The “zero” adjustment can be made manually or automatically.

1-6

INTRODUCTION

Other features include two “hold” modes, allowing either the arithmetic maximum or minimum values to be held indefinitely until reset by the user.

The meter, probes and accessories are protected when not in use by a sturdy carrying case.

APPLICATIONS

• Sorting or performing incoming inspection on permanent

magnets, particularly multi-pole magnets.

•

Testing audio speaker magnet assemblies, electric motor armatures and stators, transformer lamination stacks, cut toroidal cores, coils and solenoids.

•

Determining the location of stray fields around medical diagnostic equipment.

•

Determining sources of electromagnetic interference.

•

Locating flaws in welded joints.

•

Inspection of ferrous materials.

•

3-dimensional field mapping.

•

Inspection of magnetic recording heads.

1-7

Section 2

Specifications

INSTRUMENT

RANGE RESOLUTION

gauss tesla A/m Gauss tesla A/m

200 G 20 mT 16 kA/m 0.1 G 0.01 mT 0.01 kA/m

2 kG 200 mT 159 kA/m 1 G 0.1 mT 0.1 kA/m

20 kG 2 T 1591 kA/m 10 G 1 mT 1 kA/m

ACCURACY (including probe):

dc mode: ± 2 % of reading, ± 3 counts

ac mode: 20 - 10,000 Hz: ± 3.5 % of reading, ± 5 counts

ACCURACY CHANGE WITH TEMPERATURE (not including probe): ± 0.02 % / ºC typical

WARMUP TIME TO RATED ACCURACY: 15 minutes

MIN / MAX HOLD ACQUISITION TIME:

dc mode: 180 ms typical

ac mode: 300 ms typical

BATTERY TYPE: 9 Vdc alkaline (NEDA 1640A)

BATTERY LIFE: 8 hours typical (two batteries)

AUXILIARY POWER: 9 Vdc, 300 mA

2-1

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