PHYWE 11500.10 User manual

R
Electric field meter
1 PURPOSE AND CHARACTERISTICS
The electric field meter 11500.10 (referred to below for
brevity as the EFM) is used for investigation of the field
strength in electrostatic fields.
Furthermore, in conjunction with the voltage adapter of the
EFM, static measurement of direct voltages is possible and,
remarkably, this also applies to relatively low voltages:
measuring ranges 10/100/1000 V DC.
The handy instrument, mounted on a rod, requires a DC
supply between 14 and 18 V.
The unit has a data interface which can be connected to the
9 pole D-connector of a serial RS232 interface of a
computer by means of the supplied cable.
2 MEASUREMENT PRINCIPLE
The measurement principle of the EFM is based on the fact
that an electric field induces charges at the surface of a
conductor, the superficial charge density σof which is
proportional to the normal component Enof the field
strength Eprevailing at the conductor surface:
σ= εo·En ;(εo= 8,86 · 1012 As/Vm).
Since the electrostatic field at conductor surfaces is always
perpendicular to the surface, En= E.
A gold-plated flat electrode with six radial sectors is used as
the probe of the EFM. For measurement purposes, the
electric flux to the probe is chopped periodically by means
of a vane wheel of appropriate shape, rotating closely in
front of the measurement electrode and electrically
connected to equipment earth. Depending on the position of
the wheel, the electric flux to the probe is screened off to a
greater or lesser extent and therefore fluctuates periodically
between its maximum value and zero.
The measuring electrode is connected to equipment earth
through a high resistive load. The variation of the induced
charge produces periodic voltage pulses, the amplitude of
which is proportional to the electric field strength En. Pulses
are fed to an electronic circuit, which delivers a DC voltage
output proportional to the pulse amplitude and thus to the
field strength Enprevailing at the measurement electrode.
Any conductor brought into an electric field modifies the
original field to a certain extent; this also applies for the
EFM. In a given measurement arrangement, the field
strength Eprevailing at the measuring head is proportional
to Eo, the original field strength: Eo= kE.
If the geometry between the measuring head and the
conductors producing the field is maintained, comparative
measurements can be carried out without any adverse
effects. But measurements series in which this geometry is
varied to a certain extent are also possible, provided that
the factor kremains sufficiently constant.
Calibration of the instrument in the works takes place in a
special calibration jig; it consists of a plate capacitor, one
plate of which has a circular cut-out in the centre, in which
the measuring head of the EFM is embedded flush with the
plate. In this arrangement, the indication of the measured
value is so adjusted that it corresponds to the calculable
field strength E = U/d for a plate capacitor with voltage U
and plate spacing d. In a plate capacitor therefore, the
undistorted field is measured directly by the EFM, i.e. k=1
and E = Eo; the distance between the plates must then be
d= 100 mm. Such a capacitator arrangement can be set up
in an experiment by screwing the capacitor plate 11500.01,
which has a central hole, onto the EFM and using the
capacitor plate 06233.01  of the same size  as the
opposing plate (Fig 2).
For the electrostatic voltage measurements, a capacitor
plate  mounted on an insulating support in the voltage
adapter  is placed at a defined distance in front of the
measuring head. The field strength measured by the EFM
is then a measure of the voltage applied to the capacitor.
PHYWE SYSTEME GMBH· Robert-Bosch-Breite 10 · D-37079 · Göttingen · Telefon [phone] ·Telefax (05 51) 60 41 07
11500.10
Operating instructions
The unit complies
with the corresponding
EC guidelines.

6 Range push-button
for selection of the measuring range. The selected field
measurement range is indicated by luminous diodes.
7 Table
of the field measurement ranges and the corresponding
voltage measurement ranges when the voltage
measurement attachment is set on.
8 Measuring head
Gold-plated measuring system (d≈45 mm), consisting
of a measuring electrode with 6 equal sectors,
arranged symmetrically, a complementary auxiliary
electrode for zero adjustment and a chopper wheel with
6 vanes of appropriate shape.
The protective cap 8.1 serves to protect the sensitive
measuring system when the instrument is not in use; it
can also be used to screen the measuring head during
electrical zero adjustment.
9 Tapped holes
for screwing on the voltage adapter 10 which belongs
to the instrument, and the capacitor plate 11500.01 for
field measurements in the plate capacitor.
10 Voltage adapter
for the wattless, static measurement, of DC voltages
(Ri≈1016 Ω). The measuring ranges are selected by
key 6.
The gold-plated voltage adapter contains a capacitor
plate  matched in diameter to the measuring system 
of very high insulation resistance, mounted in a metal
screen. The voltage adapter is fixed by bolts 10.1 into
the holes 9of the EFM, so that a defined spacing is
obtained between the capacitor plate and the
measuring electrode. For measurement reasons, each
EFM has its own specific voltage adapter which is
identified by the same serial number.
11 Input for voltage measurement
Two 4 mm sockets (instrument terminals) for
application of the voltage to be measured.
Socket 11.1 is connected to the capacitor plate of the
voltage adapter, socket 11.2 is connected to the metal
screen and thus to the housing earth.
3 FUNCTIONAL ELEMENTS
The instruments has the following controls and functional
elements (Fig. 3):
1 Housing
Metal housing (70mm x 70mm x 150mm) with
detachable stem (d= 10 mm, l= 145 mm). A transverse
hole (d= 4 mm) in the stem serves for earthing the
housing.
2 knob "←0→"
for electric zero setting
3 Output "± 10 V" (Ra≥10 kΩ)
pair of 4 mm sockets to connect any voltmeter with 10
V- measurement range. It is advantageous if the zero
is in the centre of the scale, in order to indicate the
direction of the field (e. g. Analogue-Demo Multimeter
ADM 2, 13820.00). The minus output socket is
connected to the housing.
4 9 pole sub-D socket
to connect the serial interface of a computer over a
supplied cable.
5 Sockets 14...18 V
Two 4mm sockets for application of the operating
voltage to the circuit and motor electronics of the EFM.
A smoothed floating DC supply between 14 and 18 V is
necessary.
11500.10
2
Fig. 2: Calibrating set-up for the electric field meter (the illustrated unit is the
older model 11500.00).
Fig. 3: Function and operating elements
7
6
5
4
3
2
1

4 HANDLING
4.1 Starting up
A smoothed, floating DC supply voltage between 14 and
18V is to be applied to the socket pair 5, with the correct
polarity. The voltage source must be capable of being
loaded up to 200 mA; universal power supply 13500.93 or
double power supply 13520.93 are suitable. The necessary
earth contact of the EFM is conveniently connected to the
4 mm transverser hole in the housing stem. This hole can
also be used to tighten the screw fastening of the stem with
the aid of a spanner or the like.
Any continuous voltmeter of adequate measurement range
is to be connected to output 3. Output voltage increases
linearly with field intensity. Depending on the direction of the
field, it will reach +10 V or -10 V for the selected final value
of the measurement range. As an optimal solution for
demonstration purposes, we recommend Analogue-Demo
Multimeter ADM 2, 13820.00 with ±10 V- measurement
range and zero in the centre of the scale. The sign of the
pointer deflection indicates the direction of the field at the
measuring electrode: provided the moving coil instrument is
connected to output 2with the correct polarity, a positive
deflection denotes a field towards the measuring electrode,
or a positive potential with respect to equipment earth of the
capacitor plate of the voltage adapter.
Attention: when the unit is switched on, no intense field
must act on the measuring head, because this would
disturb the automatic function test. Please cover the
measuring head with the protective cap 8.1 before
switching on the unit, or, in case the voltage measuring
head 10 is used, short input 11. After switching on, the unit
is ready for work as soon as the luminous diodes for the
range display stop flashing. If flashing does not stop after a
few seconds, this shows the function test was disturbed by
electric fields. In this case, briefly switch off power supply
and switch it on again once the measuring head is free of
electric fields.
4.2 Electrical zero adjustment
Before making the measurement, electrical zero adjustment
has still to be carried out, because even if no electric field is
acting on the measuring electrode of the instrument, the
pointer of the moving-coil instrument can deviate from the
set mechanical zero-point (scale centre). The appropriate
correction of the pointer position can be carried out with the
aid of the rotary knob 2of the EFM, and most accurately
when the most sensitive measuring range is set by the
push-button 6. Naturally, the zero adjustment must be
carried out in the absence of the field to be measured.
It should be noted that, in addition to the measurement field,
stray electrostatic fields  caused by charged parts in the
vicinity  will sometimes affect the measuring head. It is true
that these fields can easily be screened off by means of the
protective cap 8.1 for adjustment purposes, but during the
actual measurement (without the cap), they would again be
effective. The existence of interference fields can be
recognised from the fact that the pointer deflections differ
considerably with and without the protective cap. As far as
possible, stray electrostatic fields should be avoided. A
slight residual field can be eliminated from the measured
result by the electrical zero adjustment.
A further factor influencing the measurement is the voltaic
potential between the measuring electrode and measuring
apparatus (environment). Of course, its field only becomes
significant when working in the most sensitive measuring
range. It can be eliminated if the electrical zero adjustment
is carried out in the experimental jig itself, which must of
course be in a discharged condition. Practical examples:
For electrostatic voltage measurements, the zero
adjustment is carried out with the voltage adapter 10
attached and short-circuited with a connection lead. In the
case of field strength measurements in a plate capacitor
similar to the calibration apparatus, with the measuring
head inserted in the hole in one plate (Fig. 2), the zero
adjustment is carried out with the capacitor plates short-
circuited.
With relatively open measuring arrangements, where the
measuring head is not screened from stray fields from the
surroundings, the pointer deflection will also be influenced
by the operator himself  e.g. when operating the rotary
knob 2; therefore one should move sufficiently far away
from the EFM in order to read the pointer position. This
applies both to the zero adjustment and the actual
measurement.
The zero drift of the EFM is relatively small and can be
practically disregarded over the time of performance of an
experiment. However, when working with an open
experimental arrangement, it should be expected that stray
electrostatic fields will vary in an uncontrolled manner or
even come into being in the course of the experiment. It is
therefore advisable to repeat the zero check from time to
time.
4.3 Treatment of the measuring system
The gold-plated measuring system (and also the capacitor
plate of the voltage adapter) should not be contaminated
and also should not be touched by hand. Above all, the
rotating chopper wheel must not be touched. For an
inexperienced observer, the rotation is not directly visible or
audible. The Teflon insultation of the voltage adapter should
also not be touched or contaminated, so that no conductive
surfaces are formed. When not in use, the sensitive
measuring system is to be covered with the protective cap
unless the voltage adapter is fitted.
4.4 Hints for working with the EFM
The EFM will be set up according to the particular
experimental requirements. The surface of the measuring
electrode should be arranged perpendicular to the direction
of the field to be investigated.
Unsatisfactory results in electrostatic experiments are
mainly due, apart from inadequate insulation of stems and
supports, to stray electrostatic fields They can be caused
not only by charged bodies which do not belong to the
actual measurement arrangement (e.g. high-voltage
sources), but also by uncontrollable charges on insulating
plastic surfaces. A few hints on the elimination of these error
sources will be given below.
The high-voltage equipment is to be set up as far away as
possible from the EFM, in order that its field disturbs the
measurement as little as possible. As far as the experiment
permits, the voltage will be switched off during the
measurement; it is generally advisable not to alter the
voltage setting for this.
Charges on the experimental bench can be eliminated or at
least reduced by spraying with an anti-static spray. Live
connectors should be prevented from coming into contact
with the bench surface. On the other hand, when the 50kV
connecting cables, 0.5 m or 1 m long, 07366.00 and
07367.00, are used, their routing is substantially uncritical.
Charges on articles of clothing containing synthetic fibres
are sometimes a very considerable source of stray fields.
Their field becomes noticeable when the wearer comes
near the EFM. It is therefore advisable not to wear such
clothing during electrostatic experiments. In any case, the
operator should remain at an appropriate distance from the
EFM when reading the measured value.
Particular attention is to be paid to the Plexiglass stems on
311500.10

N = LSB of the measurement value
X = measurement value (the corresponding value for the
final value of the measurement range is 200 bits)
R = range (4 bits in total)
0001 1 kV/m
0010 10 kV/m
0100 100 kV/m
V = sign of the measurement value (1 = negative, 0 =
positive)
Normal measurement values are recognised by the fact that
the MSB (bit 7) of byte 1 always has the value "0". If, on the
other hand, the MSB is "1", an important information is
transmitted together with the corresponding measurement
value.
6 EXPERIMENTAL LITERATURE
Experimental units in Physics:
The electric field, 1, (in German) 16100.01
The electric field, 2, (in German) 16100.11
7 TECHNICAL DATA
Operating voltage 14  18V DC
Current consumption < 200 mA
Output resistance 1 kΩ
Output voltage ± 10 V DC
Short-time drift < 1 %/h
Operating temperature 10  40 °C
Permissible atmospheric
humidity up to 65% r. H.
Housing dimensions in mm 70 x 70 x 150
Support stem d= 10 mm, l= 145 mm
Weight 0,67 kg
Field measurement
Measuring ranges 1/10/100 kV/m
Precision (calibrating set-up
according to fig. 2) ± 3%
Voltage measurement
Measuring ranges 10/100/1000 V DC
Accuracy2) ± 3%
Input resistance approx. 1016 Ω
Input capacitance approx. 10 pF
8 ACCESSORIES
Analogue demonstration multimeter ADM 2 13820.00
Capacitor plate with hole, d= 55 mm 11500.01
Set-up capacitor, large 06233.00
Power supply, universal 13500.93
or
Double power supply 13520.93
9 WARRANTY INDICATION
We grant a 6 months warranty on the unit supplied by us.
This does not cover normal wear or damages due to wrong
use.
The manufacturer only is responsible for function and safety
characteristics of the unit if maintenance, repairs or
modifications to the latter were carried out either by the
manufacturer himself or by an institution expressly
authorised by him.
which insulated conductors, e.g. conductor spheres, are
mounted. Not only is the insulation resistance reduced by
contamination or a film of moisture, but also charges, which
falsify the measurement, are often to be found on these
stems. It is therefore advisable to clean the stems before
use in lukewarm water with a detergent additive. After
drying, they can be held in clamps if necessary, so that
renewed contamination through handling is avoided. To
remove charges from the stems, they can be passed once
or twice over a flame, which will at the same time remove
any remaining moisture film. However, they should not be
too intensely heated, since otherwise the Plexiglass could
be distorted. This flame treatment should also be carried
out now and then during a measurement series and
freedom from charges should be checked with the EFM.
5 DESCRIPTION OF THE DATA INTERFACE
A PC can be connected to the unit by means of the supplied
data cable, in order to assure data output. Connection is
carried out directly to a 9 pole serial (RS232) interface
output of the computer. For connection to a computer with
25 pole connector, a commercial adapter is required.
The supplied cable has the following pin allocation, which is
the same for both connectors:
RxD = 2
DTR = 4
RTS = 7
The shielding is cut off at one of the two plugs in order to
avoid equipotential bonding currents between the computer
and the unit. In case of problems with data transfer, it must
be checked if the used cable actually is the one supplied
with the unit.
A simple programme to output measurement values is
supplied with the unit. If necessary, please ask us for the
actual status of available software.
5.1 Information for the programmer
The following interface description only is relevant for users
who wish to create their own programmes. This in any case
will require good knowledge of the RS232 interface.
RTS = 1 and DTR = 0 must be set on the computer for the
interface to work. The data will then be received at xx286,
whose serial interface is set as follows: 9600 Baud, 8
Databit, no parity, 1 Stopbit.
The unit transmits measurement data every 100 ms. These
always consist of 2 bytes following each other immediately.
In order to differentiate, the LSB (bit 0) of the 1st byte
always is "1" and the LSB of the 2nd byte always is "0". The
measurement values are transmitted with a resolution of 8
bits and a supplementary bit for the sign. The first 7 bits are
in the second byte, whereas the last bit of the first byte is
transmitted as the last but one bit (bit 1). The other bits of
the first byte give information concerning the set
measurement range and the differentiation between cases
related to the output measurement value according to the
following table:
The designation of the single bits means:
411500.10
1st Byte 2nd Byte Value Moment in time
0VRRRRN1 XXXXXXX0 Meas. value every 100 ms
1V0010N1 XXXXXXX0 Meas. value Switching off
1-0110N1 XXXXXXX0 Operating voltage Voltage too low
1V1010N1 XXXXXXX0 Meas. value Functional error
1V1110N1 XXXXXXX0 Operating voltage Switching on