RFL 750A User manual

I
--'

INSTRUCTIONS
Models
750A, AR, D & DR
GAUSSMETERS
For units with Serial Numbers above 1081
©
1976
RFL Industries, Inc.
Book No. MA-41960A

Model 750A Gaussmeter, with analog Indicator.
2
Model 7500 Gaussmeter, with digital Indicator.

Specifications .
Description
CONTENTS
4
6
Operation . . . . . . . . . . . . . . . . . . . . 10
Theory of Operation
Calibration Procedures
16
18
Troubleshooting. ................. 25
Replaceable Parts . . . . . . . . . . . . . . . . . 26
3

SPECIFICATIONS
MODel 750A
Accuracy: ±1.5% of full-scale range, plus probe accuracy to 10 kG direct
reading. Probe data supplied for fields
to 25 kG. Special probe data
available for fields above 25 kG.
Low Ranges: 0 to 0.1,0.2,0.5, 1,2,5, 10,20, 50 Gauss Full Scale.
High Ranges: 0 to 100, 200, 500, 1 K, 2K, 5K, 10K, 20K, 50K Gauss
Full Scale.
Frequency Response: (Typical)
fHz
20
100
150
200
300
400
500
600
700
800
Attenuation dB
o
.02
.05
.09
.25
.52
-1.0
-1.9
-3.4
-4.8
AC measurements are in terms of peak flux density.
4

MODEL 7500
Accuracy: ±[0.2% of reading ±1 digit), plus probe accuracy to 10 kG
direct reading. Probe data supplied for fields to 25 kG. Special probe
data available for fields above 25
kG.
Ranges: 0 to 10, 100, 1 K, 10K, and lOOK full-scale, plus 100% overrange.
Frequency Response: (Typical)
fHz
20
100
150
200
300
400
500
600
700
800
Attenuation dB
o
.02
.05
.09
.25
.52
-1.0
-1.9
-3.4
-4.8
AC measurements are in terms of peak flux density.
Temperature Effects:
Instrument: Normal temperature excursions encountered in laboratory
or typical production facility will have little or no effect on the
instrument's operation or accuracy.
Probe: Standard InAs element Hall probes will generally exhibit a
temperature coefficient of approximately
-0.1 %f'C. Probes for the
Model 750A and 7500 will have temperature coefficients no greater
than 0.1 %f'C. Typical values will be on the order of -0.06% to
-0.08%f'C.
Temperature compensated probes are available on special order with
azero drift of
less than ±0.1 Gaussf'C.
5

DESCRIPTION
RFL Model 750 Series Gaussmeters are supplied as aModel 750A
analog version, Model 7500 digital-display instrument, or as Model 750AR
or 7500R which are rack-mount versions of the standard instruments.
Models 750A and
7500 are. bench-mount instruments equipped with II
carrying handle, zero-Gauss chamber, and incorporating astorage area
for the Hall probe. All operational controls are located on the front panel.
Rear panel connectors provide a 0 to 1.5 volt dc emf proportional to the
full-scale range
of the meter, and aseparate output to enable visual display
of the magnetic field effects on an auxiliary oscilloscope.
Internal calibration
is provided in all instruments. The electronic
calibration
circuit is adjusted at the factory with instrumentation having
an accuracy
of better than 0.1 %. Traceability to the National Bureau of
Standards is assured through instrumentation checked by NBS or having
basic values obtainable through standard physics technology.
Model 750A
The analog instrument measures de and permanent magnet fields and
ac fields to 600 Hz at flux density levels up to 50,000 Gauss. Eighteen
full-scale
ranges are provided using a 1 - 2 - 5 scaling arrangement with
0.1 Gauss full-scale as the most sensitive range. A 5% inch parallax
corrected taut-band meter
with 1 GO divisions provides readout to tenths
of a scale division. Azero center scale is also provided to enhance operation
when
polarity indication is desired.
Model 7500
The Model 7500 is similar in appearance and operation to the Model
750A. A
3% digit seven segment display is incorporated providing a full
four digits at full-scale range. One hundred percent overrange is provided
as well as polarity indication of the field being measured. Bipolar circuitry
and meter indication simplify operation where fields of alternate polarity
are measured. Five full-scale ranges of 10, 100, 1000, 10,000, and 100,000
Gauss are incorporated into the Model 7500 allowing resolution of 0.01
Gauss on the most sensitive range. Decimal point location for the various
ranges is automatic through operation of the RANGE selector.
Operation
of all units is from 115 or 230 volt, 50/60 Hz, 10 watts, line
supply. Instrument
size is 11 %inches (29 cm) wide over handle, 6%
inches (16.5 em) high and 10 inches (25 cm) deep. Weight is 7pounds
(3.3
kg) for the Model 750A and 8pounds (3.6 kg) for the Model 7500.
6

Front-panel detail, Model 750A.
Front-panel detail, Model 7500.
Rear-panel detail, Models 750A and 7500.
7

.,' .
_..>1.1..-" -.1._ ...... $
Front-panel detail, Model 750AR .
..
-.-.-
-:-
~. i
"':'"".
Front-panel detail, Model 750DR •
..
--
57R?
..
!II
..
..
8
Rear-panel detail, Models 750AR and 750DR.

The 750AR and 750DR are rack mount versions of the bench instru-
ments
and incorporate all the attributes of their counterparts. In these
instruments the auxiliary outputs are available from the front panel,
and at the rear. The rack style enclosure also incorporates space to install
the 10-75 Incremental/Differential Module. The Rversions occupy 7
.inches of rack height with astandard 19 inch rack width panel.
Both the Model 750A and the Model 750D
are equipped with a37-pin
EIA connector for quick connection to the Model ID-75 Incremental/
Differential Adapter. The connector also carries the 1.5 volt, full-scale
analog signal. The mating plug
for this connector, RFL PIN HB-43774,
may
be ordered separately, and is listed on the price list.
When Option HB·43775, for BCD output, is ordered, the mating plug
is included. The mating plug is also part of the cable assembly supplied
with the Model 10-75,
and BCD wiring can be added to this cable assembly
by the buyer
if so desired.
Internal wiring
of the Model 750D for BCD output can be performed at
the factory or in the field. Awiring list is included on page 27. Awiring
harness for the BCD option can be ordered from the factory as RFL
PIN HB·43773, and the mating plug should be ordered with the harness.
BCD output is a 1 2 4 8 code, using positive logic, with standard
TTL levels of 0.4 volts max. and 2.4 volts min. for 0and 1, respectively.
The drive will sink
two standard loads, 3.2 mA in the low state.
9

OPERATING INSTRUCTIONS
1. Check line voltage marking on rear of instrument to be certain
unit
is set for proper line voltage. To change line voltage consult
instructions
at end of section on Calibration.
2. Adjust all
three BALANCE controls to the center of their rotation
(each control
is aten-turn potentiometer).
3. Set CAL control
to the center of its rotation (this control is asingle-
turn potentiometer).
4. For Model 750A set ZE RO control to the center of its rotation
(single
turn potentiometer).
5. Set GAUSS FULL SCALE RANGE selector
to lOOK on the
Model 750D. On the Model 750A place RANGE switch in HIGH
and GAUSS FULL SCALE RANGE selector on 50K Gauss.
6. Remove Hall probe container from rear of instrument enclosure
(on rack
mount instruments the probe container is not incorporated
into the enclosure). Remove probe from its container and plug it
into the Gaussmeter PROBE receptacle.
7. Plug Gaussmeter line plug into appropriate ac line power r-eceptacle.
8. Place sensing end of Gaussmeter probe into the ZE RO GAUSS
CHAMBER. Set MODE switch to AC/BALANCE and POWER
switch to ON. On th~ Model 750D the DPM segments will light,
indication should be 00.0. On the Model 750A the meter ZERO
control should be adjusted, if necessary for 0indication on upper
scale.
9. Allow
about three minutes for instrument warm-up.
10. Set RANGE selector
to 10K and adjust MEDIUM BALANCE
control for meter zero indication.
Set RANGE selector
to 1K and again adjust MEDIUM BALANCE
control for meter zero. If zero is not attainable adjust both COARSE
and MEDIUM BALANCE controls until zero is achieved.
10

11. Set RANGE selector to 10 Gauss position and adjust COARSE,
MEDIUM, and
FINE BALANCE controls until aminimum reading
is achieved. On Model 750A the RANGE switch must also be placed
in LOW position
and the RANGE selector placed in 0.1 position
after minimum indication
is achieved on the 10 Gauss range. Note:
There will
be some interaction between the controls.
12.
Set MODE switch to DC and adjust FINE BALANCE control
only for ameter reading of zero. On the Model 750D areading
of eithel'\O.OO or -0.00 is correct.
13. Model 750A
only: Set RANGE selector to 50K, RANGE switch
to HIGH, and check for zero indication of meter on upper scale.
Adjust ZERO control if necessary for zero meter indication. Return
RANGE selector
to 0.1 and RANGE switch to LOW and readjust
FINE BALANCE control
for meter zero indication.
14.
Place RANGE switch in CAL position. Adjust CAL control until
meter on Model 750A indicates full-scale. Note: Two extra pickets
are marked beyond the full-scale cardinal picket. On Model 750D
adjust
CAL control until DPM indicates 1.000. .
15.
Place RANGE selector (and RANGE switch on the Model 750A)
to settings appropriate for the measurements which will be per-
formed. Remove probe from ZERO GAUSS CHAMBER.
NOTE: The probe
tip is color coded for polarity indication purposes.
When the side colored red is facing amagnetic pole which would
attract the north seeking
end of a compass needle the meter will
deflect up-scale (to the right) on the Model 750A. The Model 750D
DPM will indicate areading with no polarity sign before the numerals.
16. In many instances
it is advisable to periodically recheck the Gauss-
meter calibration and zero condition. For calibration check merely
place the RANGE selector in
CAL position and note meter indication.
It is not necessary to remove the probe tip from the field being
measured for this check.
To check zero balance place probe
tip in the ZERO GAUSS
CHAMBER
and observe steps 4, 5, and 6above if zero indication
is not in evidence. If measurements are not of ahigh order of
accuracy any slight change in zero will not affect the readings. Under
normal conditions resetting
of the BALANCE or CAL controls
may
only be required once aday.
11

Polarity Sensing (
In DC Mode the Models 750A and 7500 are polarity sensitive. The
Model 7500 incorporates abipolar meter which automatically indicates
field polarity.
In AC Mode, the Gaussmeter will measure the peak value of a
sinusoidally varying magnetic field which has no
dc component.
The following waveforms can be observed with an oscilloscope
connected to the output terminals:
One Cycle
-'------Of AC Field
Oscilloscope output with ac field. Meter will read peak value of
field in ac mode. Carrier frequency is approximately 1 kHz.
Oscilloscope output with dc field. Meter will read 1.57 times dc
field in ac mode.
12

Oscilloscope output with ac and dc fields. Peak ac field is less than
dc field. Meter will read 1.57 times dc field in ac mode.
One Cycle
Of AC Field
Oscilloscope output with ac and dc fields. Peak ac field is greater
than dc field.
Model 750A Only
Zero-center operation. After completing step 7, foregoing, set the
RANGE selector
to 50K and the RANGE switch to HIGH al1d adjust
the Gaussmeter ZERO control
until 0indication on the lower (zero
center)
scale is achieved. This scale is calibrated 10 - 0 - 10. Thus on a
range having a scale factor of 1, for example the 10-Gauss range, end
scale readings would be 5 Gauss. On the 50 Gauss range end scale
indication would be 25 Gauss.
Probe "Turnover" Error
Due to the slight unbalances in Hall elements some degree of turnover
is evident in some probes. Turnover is indicated by a· difference in
readings in agiven field when the
polarity is reversed. For example, the
Model
7500 might indicate 85.0 Gauss with the probe in agiven field
and
-85.1 Gauss when the probe is reversed in that field. For highest
accuracy make readings
of the same polarity as indicated when the
RANGE selector
is placed in CAL position.
13

FLAT PROBES
.,..~ 1 ~.~ -r- .0'0
.~-r
.011 x,117 ~
FP.OZG-U
-Y=
OI
rT·OI.
ACTIVE AREA --y-
.040 X .0'0 e
~
FP·Q15·U
TANGENT! AL PROBE
ACTIVE AREA
.078 X .181
AXIAL PROBES
E3 t~§~ft::'-,r-
~ ~
ACTIYE: AREA ~
.078 X .117 ~
Fp·039·U
I'
"1/4
'1
-V- 5116 01'.
I
(;I~
AP-312-U
ACTIVE AREA
.010 Jl .150
'5I32D~ r-
I'
10 114
Je ACTIVE
ARJA~ a
AP·1SfoU
.062 X .125
3¥
I6,LJ"
113/4
~.200
-rJ
AP-ZOo-U
ACTIVE AR~
.060 X .150
3DIA.
I6
L
I'
113/4
,.'OO-,r--
~
• t
ACTIVE ARE~
AP-lOD-U
.030 X .060
DIFFERENTIAL AXIAL PROBE
2 112 -- ... ·"'tl-_---:--=-.--_---_-- __ - __ -_--_---:-_-: : :_'~2 __ -n : -: u : : --~v
AD-312·U ~:bYi .~~A
NOTES:
1. Awide range of probe configurations available for special applications on request.
2. All pmbes are supplied with a 5 foot cable. Extension cables available.
14

TERMINAL
FUNCTIONS - ACCESSORY CONNECTOR J1
MODELS 750A and 7500
TERMINAL FUNCTION TERM IN
DPM - J3
1J2 - 3
2J2 - 4
3J2 - 7
4J2 - 6
5Probe Balance
6
Probe Balance
7
Attenuator Ground
8Chassis
Ground
9Digital
and BCD Ground N
10 BCD 800
Output 9
11
BCD 400 Output
11
12 BCD 200
Output
12
13 BCD 100
Output
K
14
BCD 8 Output
5
15 BCD 4
Output
F
16
BCD 2 Output
6
17
BCD 1 Output
E
18
Hold D
19
Print Command
3
20
J2 - 1
21
J2 - 2
22
J2 - 8
23 J2 - 9
24
Analog Output 1.5V Full-Scale
25
Power Supply Ground
26
+15V Output
27
-15V Output
48
Polarity
4
29
BCD 1000 Output
14
30 BCD 80
Output
7
31
BCD 40 Output
J
32 BCD
20 Output
8
33 BCD 10
Output
4
34
35
36
37
Outrange
C
Terminals of Jl which are associated with J3, in the foregoing, are wired at
the factory when Option HB-43773, providing BCD output, Is ordered.
15

THEORY OF OPERATION
Refer to Block Diagram, Figure 1and the Hall effect, page 17.
The oscillator generates a
constant voltage, near 1035 Hz, which is
converted to a constant current for the Hall probe drive. Aseries of
Balance controls is used to compensate for probe element electrical
unbalance and for
any in-phase and quadrature unbalance in the Gauss-
meter electronic circuitry.
The
emf generated in the probe by amagnetic field is fed to the
Range Attenuator where it is scaled to permit measuremenH over the
various ranges. The following amplifiers raise the Hall emf to auseable
value.
The Calibration Control and probe level setting resistors are part of
the amplifier circuit.
In the AC/BALANCE MODE the signal is filtered to remove oscillator
harmonics, and
any line-frequency 'components, and is detected with a
precision operational rectifier.
In DC MODE the signal is sensed with
asynchronous detector provid ing an output proportional to both amplitude
and polarity
of the magnetic field.
In the Model 750A the output of either the operational rectifier or
synchronous detector drives asubsequent amplifier which has aZERO
control
to enable either zero left or zero center operation. In the Model
7500 the detector output(s) drive the DPM directly.
Col
f" - --- - - - - - - - -- - ---- ---,
I Z,ro I
I I
>--+-iL __ Y-I~~t:.:J iI
I
I
I
I Output' I
L. ~O~~25~A J
r----------------
I
I
I
1
I
I
I Aceeaory
I
: Output 1
I MO DEL 1500 I
LJ
16
Figure 1. Block Diagram, Models 750A and 7500

The Hall Effect
When electrons move in aconductor or semiconductor perpendicular
to amagnetic field, they are deflected to one side of the conductor (left
or right depending on the polarity of the field) in a direction normal to
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 (or semiconductor) to establish atransverse electric
field which opposes
further deflection of charge carriers.
H
E
II
The magnitude of tHis potential is given by:
E= RIH
t
where, E is the Hall voltage, I is the current in amperes, H is the',magnetic
flux density in Gauss, t is thickness in cm and R is the Hall coefficient.
17

CALIBRATION PROCEDURES
General: Under conditions of ordinary use, it is recommended that
the zero and full-scale points of the Models 750A and 7500 be checked
daily, as aminimum. When working with low-level fields, it may be
advisable
to check the zero more frequently. These adjustments are
described
in the "Operational Instructions" of this manual.
Test Equipment: For more extensive adjustments, the following test
equipment
is recommended:
a. Adigital ac and dc voltmeter, with six-digit readout, and with
dc
ranges of 0.1, 1.0, 10, and 100 volts full-scale, ±0.02%; ac ranges
of 1.0, 10, and 100 volts, full-scale, iO.25%.
b. An. oscilloscope with vertical response of at least 1MHz ±3 dB,
sensitivity
of at least 1 mV per cm, and with commensurate hori-
zontal time base.
c. Afrequency counter with capability to several kHz, and with
sensitivity ranges
of 0.1, 1.0, and 10 volts.
d. Aresistance decade with resolution
of 0.1 ohm and with maximum
resistance
of at least 10K ohms.
e. Reference magnets with fields of 10, 50, 100, 200, 500, 1000,
5000, 10,000 and 20,000 Gauss. Accuracy
of reference magnets
affects accuracy
of calibration. .
f. Aprecision solenoid, or Helmholtz coil, with arange of at least
0.1
to 20 Gauss.
g. An ac reference magnet with afield of 1000 Gauss. Accuracy of
reference magnet affects accuracy of calibration.
Oscillator Adjustment: This adjustment may be necessary if components
of the oscillator circuit are replaced. It is accomplished as follows:
1. Insert standard FP-039/U Probe into Probe Socket.
2.
voltmeter between TP-17 (high) and TP-12 (ground).
ntil voltmeter reads +7.500 ±0.1% volts.
3. Connect frequency counter between
TP-l0 (high) and TP-12
(ground), and adjust R1
for frequency of 1035 ±3 Hz.
18