Magnet-physik FH 55 User manual

BA - Nr.: 2000550EBA01
Emil-Hoffmann-Str. 3
50996 Cologne
Germany
Operating Instructions
FH 55
Gauss-/Teslameter
Preserve for future application!

Gauss- / Teslameter
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SEPTEMBER,24TH,2019
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Introduction
Dear customer,
You have decided on a product of high technical standard from MAGNET-PHYSIK. We are
convinced that our product will be a valuable help in your daily work. Condition is that the
operating instructions are read carefully and observed. We will not take over any warranty or
liability in case of deliberate faulty operation or disregard of our safety notes.
If you face any problems while working with the equipment or the operating instructions or if
you have any proposals for improvements please do not hesitate to contact us.
Purpose
The operating instructions give a survey about the application and functionality of the FH 55
Gauss-/Teslameter.
Target Group
In the following chapters the user of the devicet will find all necessary information regarding
handling and operation.
Address
MAGNET-PHYSIK
Dr. Steingroever GmbH
Emil-Hoffmann-Str. 3
Tel. :
[phone]
50996 Köln, Germany
Fax. :
[phone]

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Notes
•This instruction cannot cover every possible aspect of installation, operation and
maintenance, or every error that might occur.
•If you would like more information, or if you encounter particular problems that are not
discussed in sufficient detail in the instructions, please contact company MAGNET-
PHYSIK.
•We also state that the content of these Instructions is not part of a previous or existing
agreement, undertaking, or legal relationship, and is not intended to amend the same. All
obligations of MAGNET-PHYSIK result from the applicable warranty: These contractual
warranty provisions are neither extended nor limited by statements in these instructions.
MAGNET-PHYSIK GmbH, Köln -
2000550EBA01/2019
Passing on and reproduction of these documents, and utilization
and disclosure of their contents is prohibited unless specifically
authorized. Violations shall be cause for damage liability.
All rights reserved.
Subject to change without prior notice
Although the contents of this publication have been checked for
agreement with the hardware and software described, we do not
accept liability for total agreement since differences cannot be
completely excluded. The information in this publication is
checked at regular intervals and necessary corrections included in
the next release. Your suggestions for improving this publication
are welcome.

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Table of Contents
1General Information ....................................................................................................6
1.1 Safety Instructions ...............................................................................................6
1.2 Intended Purpose..................................................................................................6
1.3 Sources of Danger................................................................................................7
1.4 Authorized Operator ............................................................................................7
1.5 Safety Measures at Place of Installation..............................................................7
1.6 Safeguard Installations.........................................................................................8
1.7 Emergency Measures...........................................................................................8
2Transport and Installation...........................................................................................9
2.1 Unpacking and Checking.....................................................................................9
2.2 Transport and Storage..........................................................................................9
2.3 Technical Data.....................................................................................................9
3Introduction ..................................................................................................................11
3.1 General.................................................................................................................11
3.2 Description...........................................................................................................12
4Operation.......................................................................................................................14
4.1 Initial Setup..........................................................................................................14
4.2 Standard Display..................................................................................................15
4.3 Keys .....................................................................................................................15
4.4 Probe Handling....................................................................................................17
5Functions.......................................................................................................................18
5.1 AC/DC.................................................................................................................18
5.2 Range ...................................................................................................................18
5.3 Auto .....................................................................................................................18
5.4 Zero......................................................................................................................19
5.5 Filter.....................................................................................................................19
5.6 Unit ......................................................................................................................19
5.7 Temp....................................................................................................................20
5.8 Limit.....................................................................................................................20
5.9 Reset.....................................................................................................................21
5.10 Max./Min. ............................................................................................................21
5.11 Peak......................................................................................................................21
5.12 Relative................................................................................................................21
5.13 Field Correction (Menu function)........................................................................22
5.14 Temp. Correction (Menu function)......................................................................22
5.15 Remote Access (Menu function) .........................................................................22
5.16 Remote Baud Rate (Menu function)....................................................................22
6Probes ............................................................................................................................23
6.1 Changing Probes..................................................................................................23

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6.2 Probe handling.....................................................................................................23
6.3 Probe Operation...................................................................................................24
6.4 Probe Types .........................................................................................................24
6.5 Probe Sensitivity and Measuring Ranges ............................................................26
6.6 Probe Accuracy....................................................................................................26
7Remote Operation ........................................................................................................28
7.1 Access Rights.......................................................................................................28
7.2 Command Format for the Serial Interface...........................................................28
8Maintenance..................................................................................................................33
8.1 Maintenance Plan.................................................................................................33
8.2 Checking for Damage..........................................................................................33
8.3 Calibration ...........................................................................................................33
8.4 Troubleshooting...................................................................................................33
8.5 Connectors ...........................................................................................................34
8.5.1 Probe Connector ..............................................................................................34
8.5.2 Analog Output .................................................................................................34
8.5.3 Serial Interface RS 232....................................................................................34
8.5.4 Relay Output for Limits...................................................................................35
8.6 Accessories ..........................................................................................................36
8.7 Taking Out of Operation ation.............................................................................36
List of Tables
TABLE 1:AMBIENT CONDITIONS ...................................................................................................9
TABLE 2:ELECTROMAGNETIC TOLERANCE (EMV).....................................................................10
TABLE 3:DETAILS ON IEC- /VDE-SAFETY.................................................................................10
List of Illustrations
FIG.1:GAUSS-/TESLAMETER FH 55............................................................................................12
FIG.2:MAGNETIC SHIELDING CHAMBER NK 1 ............................................................................14
FIG.3:PROBE ORIENTATION FOR POSITIVE READING ...................................................................24
FIG.4:SURFACE FIELD PROBE......................................................................................................25

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1General Information
The magnetic field strength meter FH 55 is a compact benchtop instrument for measuring the
magnetic field strength Hin Ampere per Meter (A/m) and the magnetic flux density or
induction Bin Tesla (T) or Gauss (G). Particular features of the FH 55 are high accuracy, easy
handling and a multitude of functions.
1.1 Safety Instructions
Special warning signals, whose non-observance may lead to injuries and/or property damage, as
well as important tips are indicated in these operating instructions as follows:
Danger!
means that serious bodily injury resulting in death or considerable material
damage may occur if the appropriate safety measures are not taken.
Caution!
means that light bodily injury or material damage may occur if the
appropriate safety measures are not taken.
Important!
Indicates important information which is to be paid particular attention.
1.2 Intended Purpose
Important!
It must be explicitly stated that the field strength meter FH 55 is to be used
only for its intended purpose.
The intended purpose of the FH 55 is the measurement of the magnetic
field strength or flux density of static, periodically alternating or pulsed
magnetic fields.
Every application not in accordance with this intended purpose is absolutely
prohibited and implies the deliberate dealing with non-calculable risks for
both the operator as well as the equipment.
Unauthorized reconstruction of and/or alterations to the equipment are
strictly forbidden!
The instructions as stipulated in this operating manual for operation and installation are to be
strictly observed!

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1.3 Sources of Danger
The field strength meter FH 55 is operated with battery power or with a special mains power
supply. At this point, for reasons of work-place safety and accident prevention the sources of
danger emanating from such a device will be especially pointed out. The respective instructions
to the operator and owner of the field strength meter are to be strictly adhered to.
Danger!
Under no circumstances the equipment must come into contact with liquid
mediums, such as water, oil, etc. If in spite of all precautions taken, such a
medium does come into contact with the electronics of
the FH 55, there is considerable danger for the smooth operation of the
device!
In this case the device must be shut down immediately by pulling the line
power plug.
The equipment must similarly be switched off when being cleaned. Never
clean with water! Dry cloths only to be used for cleaning!
Danger!
The Hall probe must never be brought into contact with an electrical voltage
conductor. The paint on the probe surface is not an electrical insulation.
Disregard of this warning can cause danger to life of the user. Additionally,
the device and the probe can be damaged.
Danger!
Do not operate the device in an explosive atmosphere:
Do not operate the instrument in the presence of flammable gases or fumes.
Operation of any electrical instrument in such an environment constitutes a
definite safety hazard.
1.4 Authorized Operator
The field strength meter FH 55 may only be used and connected by personnel authorized by
owner.
The owner must in this case:
•place operating instructions at the operator's disposal at all times and
•make sure the operator has read and understood them.
1.5 Safety Measures at Place of Installation
No special safety measures are necessary.

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1.6 Safeguard Installations
The device does not have any special safeguard installations as safety concerns have been
considered in construction. A potential danger only arises if the device is used against its
intended purpose of operation or safety regulations are disregarded.
1.7 Emergency Measures
In the case of emergency, when all safety instructions fail, proceed as follows:
Important!
1. Take emergency measures, such as “First-aid”.
2. Secure the device and working place against further use.
3. Write the case report.

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2Transport and Installation
2.1 Unpacking and Checking
Check the packaging for signs of damage. Any correspondence regarding damage (evident or
hidden) or partial loss of the consignment must be made in written form immediately after
receipt of goods. Also inform the freight forwarder immediately.
Open the packaging. A packing list is enclosed which enables you to check that the ordered
device and accessories have been received. Use the packing list to check that all parts of the
device have been unpacked. Check them for damages. Make sure everything has been removed
before discarding the packaging.
If the device has been damaged in transit, make sure the forwarder and insurance are informed.
Inform Magnet-Physik of the same. If there are parts or accessories missing, let Magnet-Physik
know immediately. Magnet-Physik cannot accept responsibility for any missing parts if not
informed within 60 days from date of dispatch.
Important!
Check on receipt of goods and before taking the device or accessories into
operation whether they show visible signs of damage. The device must
otherwise not be put into operation before being cleared by an authorized
person.
2.2 Transport and Storage
Always use suitable packing or containers for transport and storage, so that damage is avoided.
If possible, the original packing should be used for dispatch.
Due to their fragility, most probes are dispatched in special covers or foamed packaging. The
same packaging should be used for storage and when the probe is shipped for calibration or
repair.
Do not store the device in places where one or more of the limiting values for the ambient
conditions are exceeded.
2.3 Technical Data
Table 1 : Ambient Conditions
Temperature:
- for operation
0 °C to + 40°C
- for storage and transport
Class 1K4 according to EN 50178
25 °C to +55 °C

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Relative humidity:
- for operation
Class 3K3 according to EN 50178
5 % to 85 % (indoor), no dew,
1 g/m3to 25 g/m3
- for storage and transport
Class 1K3 according to EN 50178
5 % to 95 % (indoor), no dew,
1 g/m3to 29 g/m3
Air pressure
- for operation
Class 3K3 according to EN 50178
86 kPa to 106 kPa
- for storage and transport
Class 2K3 according to EN 50178
70 kPa to 106 kPa
Pollutants:
- SO2
0,5 ppm
(rel. humidity 60%, no dew)
- H2S
0,1 ppm
(rel. humidity 60%, no dew)
Oscillations:
according to IEC 68-2-6
10 ... 55 Hz (const. amplitude 1,0 mm),
57 ... 150 Hz (const. acceleration 2 g)
Table 2 : Electromagnetic Tolerance (EMV)
Immunity from discharge of static electricity:
based on EN 61000-4-2
Air discharge: 8 kV
Contact discharge: 4 kV
Immunity from incident high frequency:
based on EN V 50141
0.15 to 80 MHz
10 V/m
80 % AM (1 kHz)
Table 3 : Details on IEC- / VDE-Safety
Measurement of insulation based on VDE 0160 (05.88):
between electrically independent circuits and with a central
grounding point for connected circuits
- Testing voltage
at a rated voltage of the circuit (AC/DC)
Ue= 0...50 V
500 V, sine, 50 Hz
Safety test:
IEC 204-1;
VDE 0113 Part 1 (06.93)
Important!
The FH 55 must always be placed on a solid base.
Never operate the equipment in places where one or more of the limiting
values for the ambient conditions are exceeded.

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3Introduction
3.1 General
The FH 55 Gauss-/Teslameter is measuring instrument that provides measurements of AC and
DC magnetic fields using Hall sensors. The unit is designed for wide range, high accuracy, and
ease of use. The instrument is operated by front panel keys or the RS232 interface. Most user
features are one pushbutton away. The settings are stored if the instrument is switched off. The
FH 55 features:
•Magnetic Field Measurement:
−High accuracy with high resolution
−Auto range function
−DC or AC field measurement
−Individual linearization of Hall Probes
−Temperature compensation of Hall Probes
•Alphanumeric Display:
−¾ -digit display, 1 part in 3000 resolution on all ranges
−Liquid crystal display.
•Other Major Operating Functions:
−Display Filter
−Tesla, Gauss or Ampere/Meter units
−Max Hold, Min Hold
−Peak measurement
−Relative Reading
−Limit function
•Output:
−Serial Interface (RS-232C)
−Monitor Analog Output
•Probe Compatibility:
−Standard Probes with small active area –3 mT to 3 T Full-Scale Ranges
−High Field Probes to 30 T Full-Scale Range
−High Sensitivity Probes –30 µT to 300 µT Full-Scale Ranges
If you have just received your new FH 55, please proceed to the next chapter and become
familiar with the installation instructions. Complete and detailed instrument operational
information is contained in chapter Functions. Chapter Probes contains important information
concerning the choice and operation of the Hall probes. The chapter Remote Operation
describes the use of the serial interface. Basic service hints and the rear panel connector

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definitions are contained in chapter Service. Additional details on FH 55 accessories and probes
are provided in Chapter Accessories.
We welcome your comments concerning this manual. Although every effort has been made to
keep it free from errors, some may occur. When reporting a specific problem, please describe it
briefly and include the appropriate paragraph, figure, table, and page number. The material in
this manual is subject to change without notice.
3.2 Description
The FH 55 is an accurate, full-featured gaussmeter. It covers a wide range of magnetic fields
and applications. The instrument provides the user with easy-to-use front panel programming
and incorporates a liquid crystal display. The alphanumeric format allows for message-based
front panel operation. Most operations can be performed and monitored through the front panel
keypad. Some rarely used functions can be accessed through a menu.
Fig. 1 : Gauss-/Teslameter FH 55
The FH 55 measures the magnetic flux density (induction) either in Tesla (T) or Gauss (G) or
the magnetic field strength in Ampere per Meter (A/m). Magnetic field ranges can be set
manually or with auto ranging. The instrument measures both DC (static) and AC (periodically
alternating) magnetic field values. In DC operation, the display shows the DC field at the probe
with the sign (field orientation) followed by the appropriate field units. In AC operation, the
display shows RMS or Peak value for the field at the probe. The values are available over the
Serial Interface and also the Analog Output. This Analog Output allows the user to observe the
actual magnetic field waveform on an oscilloscope.
The Max./Min. function captures and displays the largest field magnitude seen since the last
Reset. The maximum value is shown in the second display line while the upper display line
contains the live field reading. Alternatively, also the highest and the lowest value can be

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displayed. The Peak function allows in DC mode the peak value of a pulsed magnetic field to
be measured.
The relative function is intended to let the user see small variations in larger fields. The user
defined set point becomes the center or zero point of the relative reading and is shown on the
second line of the display. The difference from the set point or the relative reading appears in
the top display line.

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4Operation
4.1 Initial Setup
To take the FH 55 into operation proceed as follows.
1. Power line connection: connect the power cord to the power connector on the rear side of the
instrument and to a power outlet.
2. Probe installation: Plug the probe into the connector at the front panel of the field strength
meter. Use the side screws to secure the connector.
3. Make sure that all required connections are made before you switch on the instrument
(interface, analog output, power supply)
4. Switch on the FH 55. The display lights up.
5. After initialization the display will return to the state it was in before being switched off. For
best results, the instrument and probe should warm up for at least 5 minutes before zeroing
the probe, and at least 30 minutes for rated accuracy. The probe and the shielding chamber
should be at the same temperature.
6. Place the probe in the magnetic shielding chamber and press the Zero key on the front panel.
Fig. 2 : Magnetic shielding chamber NK 1
7. Press the Enter key. The message Adjusting Zero is shown until the normal display appears
again. Do not move the probe while the Adjusting Zero message is being displayed.
8. If the unit has performed well to this point, the unit is functioning properly. If you have a
reference magnet available, you can continue with the test using the magnet to verify the
accuracy of the FH 55.
9. If continuing the procedure with a reference magnet, ensure the probe can accommodate the
range of the magnet. Use the Range key to select the proper range (or press Auto for
automatic ranging). Set the display for DC. Finally, since orientation of the probe is very
selective, press the Max./Min. key once. This will capture additionally the highest reading.
Caution!
Care must be exercised when handling the probe. The tip of the probe is very
fragile. Any excess force may break the probe.

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Probe readings are dependent upon the angle of the tip in relation to the magnetic field. The
greater the angle between the probe and the field, the higher the percentage of error. For
example, a 5° angle will cause a 0.4% error, a 10° angle will induce a 1.5% error.
9. Carefully place probe in contact with reference magnet. You may have to hunt around a bit
for the maximum reading.
For this example, we are using a 250 mT ± 1% reference magnet. In the top line the actual
reading of +198 mT is displayed. In the second line the measured maximum value of
201 mT is shown, which is within the tolerance of the reference magnet. The top line will
keep changing as the probe moves, but the bottom will remain fixed on the highest reading.
To capture a new maximum value, press the Reset key.
Once this short checkout procedure is successfully completed, the unit is ready for normal
operation. Please proceed to the following chapter for further operational information.
4.2 Standard Display
During a measurement, the actual reading is shown in the top line of the display in bright
characters. Numerical value and unit are displayed.
In the second line the outputs of several special functions are shown, e. g.
−Maximum or maximum and minimum, if the Max./Min. function is activated
−Probe temperature, if a probe with temperature sensor is connected and the Temp. Function
is activated
Always the output of the function that was activated (switched on) last is shown. If it is
deactivated (switched off), the output of the previously active function is displayed again.
The two lowest lines serve to show several information:
−Measuring mode AC or DC
−Selected range
−Rel, if relative reading is switched on
−High / Low / OK, if the limit function is switched on
−Filter, if the Filter function is switched on
−Remote-State (R): the instrument is being controlled from the interface
4.3 Keys
For the input of numerical values the numerical keypad is used. It consists of the keys 0 to 9,
the +/- key and the decimal separator.
The most important functions can be accessed directly from the standard display via function
keys. The functions are noted above the keys.
Here follow only brief descriptions of the key functions. Detailed descriptions you can find in
the next chapter (Functions).
AC/DC Toggles between AC (periodic) and DC (static) magnetic field
measurement.

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Range Allows to select the field measurement range. The available ranges depend
on the probe type.
Auto Switches on the auto range function
Zero Used to zero offsets of ambient low-level field, or from the probe. When
the user pushes the Zero Probe key, Zero Probe and "Press Enter to start"
will be displayed. The user may than press the Enter key to begin the zero
probe routine. The unit then automatically accepts whatever residual field
it reads as a zero offset, forcing the display to zero. Zero Probe is normally
activated if the probe is placed in the shielding chamber. It can also be
activated with the probe outside of the chamber to suppress ambient
magnetic fields. After some time, the display returns to normal reading.
Filter Switches Filter on and off.
Unit The FH 55 can display the magnetic flux density (induction) B in Tesla (T)
or Gauss (G) or the magnetic field strength H in Ampere per Meter (A/m).
By pressing the unit button, the user can select between these units.
Temp. Switches probe temperature display on or off. This function is only
available, if the probe has a built-in temperature sensor.
Limit This key is used to invoke a small menu that allows to activate, deactivate
and configure the limit function.
Max./Min. Turns the Max./Min. feature on and off. Max./Min. captures and displays
the absolute value of the highest field reading or the smallest and highest
reading.
Peak Allows the measurement of the maximum of peak magnetic fields or the
peak value of AC fields.
Reset Works with the Max./Min. and the DC Peak function. Resets the reading
back to zero to capture the next reading.
Relative This key is used to invoke a small menu that allows to activate or
deactivate relative function and to set the relative value.
Mode Switches between the standard display and the main menu. In the menu
additional functions can be invoked.
Enter Used to accept the numbers displayed during numerical entry.
Escape The Escape key is used to terminate a function without making changes to
the existing settings. The unit will the return to normal operation.
Delete Used to erase numerical inputs

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Inside a menu dialog Delete, Enter, Mode and Escape have the following functions:
With the Delete key you erase the last numerical input.
With Enter you confirm the last input and take over the setting. After the last input in a dialog
you leave it with Enter.
With Mode you return from a dialog directly to the measurement display. The settings are taken
over.
With Escape you go back one step in the operation. The last input gets not valid.
Numbers are input by the numerical keypad.
4.4 Probe Handling
To avoid damage and for best results during use, the probes have a number of handling and
accuracy requirements that must be observed.
An Electrically Erasable Programmable Read Only Memory (EEPROM) is included in each
probe. The EEPROM stores specific information that the gaussmeter requires for operation. The
information includes serial number and probe sensitivity, and may also include field and
temperature compensation data.
When the probe is connected, the probe memory is downloaded to the gaussmeter. This is how
the gaussmeter knows which ranges are available and which error correction to apply. To
change probes, remove the existing probe carefully, and then plug in the new probe.
Caution!
Care must be exercised when handling the probe. The tip of the probe is very
fragile. Stressing the Hall sensor can alter its calibration. Any excess force
can easily break the sensor. Broken sensors are not repairable.
Although every attempt has been made to make the probes as sturdy as possible, the probes are
still fragile. This is especially true for the exposed ceramic tip of very thin probes. Care should
be taken during measurements that no pressure is placed on the ceramic tip of the probe. The
probe should only be held in place by securing at the handle. The probe stem should never have
force applied. Any strain on the ceramic substrate may alter the probe calibration, and excessive
force may destroy the Hall sensor.
Avoid repeated flexing of the sensor mounted at the end of a flexible stem. Force should never
be applied to the tip of the probe. On all probes, do not pinch or allow cables to be struck by
any heavy or sharp objects. Although damaged or severed cables should be returned for repair,
please understand that probes are not always repairable.
When probes are installed on the instrument but not in use, the protective tubes provided with
some probes should be placed over the probe stem in order to protect the tip. When the
gaussmeter is not in use, the probes should be stored separately in some type of rigid container.
The foam container that some probes are shipped in may be retained for probe storage.

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5Functions
In the present chapter all functions of the FH 55 are described in detail. The most important
functions can be accessed directly over function keys. Some rarely used function can be
invoked in a menu. This main menu is accessed with the Mode key. The submenus are selected
with the arrow keys (, ) and opened with the Enter key.
5.1 AC/DC
With this key the user can select between AC (periodically alternating) and DC (static)
magnetic field measurement. Every push changes to the other field type.
A DC magnetic field is for example generated by a permanent magnet or by a DC current
flowing in a coil. An AC magnetic field is generated by an AC current in a coil.
In DC-mode the static magnetic field value is shown together with sign and unit. The value can
also be read from the serial interface and the analog output.
In AC-mode the RMS (root mean square) value of the field strength or flux density is displayed
unless the Peak key is not pressed (see below). The AC RMS reading is a measurement of true
RMS, defined as the square root of the average of the square of the field function taken through
one period. A DC component will be rejected if it is not large enough to overload the selected
range.
When changing to AC or DC, previously established Relative and Limit set-points are
maintained.
The functions Max./Min. and Peak are switched off when changing to AC or DC, as they
operate different in both modes.
5.2 Range
Pressing the range key opens a menu that allows to select one of ranges that are available for
the connected probe. The actually selected range is shown inversely. Select the desired range
with the arrow keys. Press Enter to confirm your choice or press Escape to return to the
previously selected range.
5.3 Auto
By pressing Auto, the Auto Range mode can be activated. In this mode, the FH 55 selects
automatically the range with the best resolution for the field to be measured. It can take up to 2
seconds for Auto Range to work, so manual ranging may be better in some conditions.
Auto cannot be used together with the functions Peak and Max./Min.
Auto Ranging should not be used when measuring small fields in large background field, i.e.,
measuring a small DC field in presence of a large AC field, or measuring a small AC field in
the presence of a large DC field.

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5.4 Zero
The Zero function sets the display to zero. It is used to zero offsets of ambient low level field or
from the probe. Zero Probe is normally activated if the probe is placed in the shielding
chamber. It can also be activated with the probe outside of the shielding chamber to suppress
ambient magnetic fields, e.g. the earth magnetic field.
For best results, the instrument and probe should warm up for at least 5 minutes before zeroing
the probe, and at least 30 minutes for rated accuracy. The probe and the magnetic shielding
chamber should be at the same temperature.
When you push the Zero key, "Zero Probe" and "Press Enter to start" will be displayed. Place
the probe into the shielding chamber, that the probe tip is approximately in the middle. Do not
touch the end of the shielding chamber with the probe tip, some very sensitive probe may even
be damaged by this. Then press the Enter key to begin the zero probe routine. The unit then
automatically accepts whatever residual field it reads as a zero offset, forcing the display to
zero. The time needed for the zero routine depends on the number of ranges that are available
for the specific probe. It may take several seconds. Do not move the probe until the normal
display appears again.
Zero should be periodically executed, especially if the most sensitive ranges are used. If you
want to suppress large magnetic fields, you should use Relative instead of Zero.
The obtained zero setting remains stored for the probe if the instrument is switched off.
5.5 Filter
The Filter function is used to achieve a quieter reading. It makes the display better readable, if
the probe is exposed to a noisy magnetic field. Be careful, if Filter is switched on and changing
magnetic fields shall be measured, as peaks are evened out and the instrument reacts slower.
The Filter function of the FH 55 is configured, that slowly changing fields are displayed and
noise is suppressed.
5.6 Unit
The FH 55 displays the magnetic flux density (induction) B in Gauss (G) or Tesla (T) or the
magnetic field strength H in Ampere per Meter (A/m). With the Unit key you can select the
desired unit. Every push changes to another unit. Between the units and their multiples there are
the following relations:
Magnetic Flux Density B:
Magnetische Feldstärke H:
1T = 1000 mT = 1000000 µT
1 T = 10000 G
1 kG = 1000 G = 1000000 mG
1 kA/m = 1000 A/m = 10 A/cm
1 A/m = 0,001 kA/m = 0,01 A/cm
1 A/cm = 0,1 kA/m = 100 A/m
1 MA/m = 1000 kA/m = 1000000 A/m
The relation between the magnetic flux density B (in „Tesla“) and the magnetic field strength H
(in A/m) is given by the following relation:
B= µ0· H= 4 · · 10-7 Vs/Am · H1.257 · 10-6 Vs/Am · H.

Gauss- / Teslameter
FH 55
BA - Nr.: 2000550EBA01
SEPTEMBER,24TH,2019
Page 20
Here µ0is the magnetic field constant or permeability of the vacuum.
When the units for field measurement are changed, relative and limit set-points are converted to
the new units with no interruption in operation.
The units T and A/m belong to the international unit system SI (Système international d'unités)
which is provided by law in many countries. The unit G belongs to the old CGS (Centimeter,
Gram, Second) unit system that is frequently used until today.
5.7 Temp.
The Temp. dialog allows to switch on or off the display of the probe temperature. Additionally,
you can select between the display in °C and °F. The function is only available, if the probe
connected to the instrument contains a temperature sensor. As the probe is heated by the control
current, the probe temperature usually will be slightly higher than the ambient temperature.
The FH 55 is no temperature measuring instrument. Do not use the probes for temperature
measurement. Extreme temperatures and mechanical stress due to fast temperature changes can
alter the calibration or destroy the Hall sensor.
5.8 Limit
The Limit function gives an optical signal, if the measured value is inside or outside a user
defined range. Two limits can be set.
The displayed texts have the following meaning:
−Low: the measured value is below the lower limit
−OK: the measured value is between the upper and the lower limit
−High: the measured value is above the upper limit
Pressing the Limit key calls up a small menu dialog. Selections can be made by the arrow keys
and Enter. Select On or Off to activate or deactivate the function.
Limit can be operated in two modes. These can be chosen by selecting the mode command
with the arrow keys and pressing Enter.
The first mode is +/-. In this mode the sign of the measured value is considered when evaluating
measured values with regard to the limits. In this way for example magnets can be sorted for
their orientation.
The second mode abs. In this mode the sign of the measured value is not considered. Only the
absolute value is evaluated. In this way for example magnets can be sorted for their field
strength, regardless of the orientation.
Before the Limit function can be used, the limit values must be defined. Therefore, select Set.
The actual setting is displayed. The actual range is the range used last. If you want to enter a
limit value in another range, press the Range key until the desired range appears. Use the
numerical keypad to enter the desired high limit point. After you have entered the value press
Enter to confirm the input.
The menu changes to the low limit point. Use the numerical keypad to enter the desired low
limit point. As soon as you press the Enter key, the Limit function is activated.