Pasco Scientific ES-9054B User manual

Instruction Manual and
Experiment Guide for
the PASCO scientific
Model ES-9054B
012-03175E
3/93
©1987 PASCO scientific $7.50
ELECTROMETER
scientific
OUTPUT GND INPUT
Model ES-9054B ELECTROMETER
PUSH
TO
ZERO
POWER
OFF ON
FUNCTION
3
10
30
100
B1 B2
ZERO ADJUST
D
C
V
O
L
T
S
ZERO
LOCK

012-03175E Electrometer
i
Table of Contents
Section Page
Copyright and Warranty..................................................................................ii
Equipment Return ...........................................................................................ii
Introduction .....................................................................................................1
Operation .........................................................................................................1
Setup ..........................................................................................................2
Measuring Charge .....................................................................................3
Measuring Voltage ....................................................................................4
Measuring Current ....................................................................................4
Using a Projection Meter ..........................................................................5
Maintenace ......................................................................................................5
Battery Installation....................................................................................6
MOS-FET Replacement ............................................................................6
Schematic ........................................................................................................7
Parts List..........................................................................................................8
Technical Support ............................................................... Inside Back Cover

Electrometer 012-03175E
Copyright Notice
The PASCO scientific 012-0xxxy Model Name manual
is copyrighted and all rights reserved. However,
permission is granted to non-profit educational institu-
tions for reproduction of any part of the manual
providing the reproductions are used only for their
laboratories and are not sold for profit. Reproduction
under any other circumstances, without the written
consent of PASCO scientific, is prohibited.
Limited Warranty
PASCO scientific warrants the product to be free from
defects in materials and workmanship for a period of
one year from the date of shipment to the customer.
PASCO will repair or replace at its option any part of
the product which is deemed to be defective in material
or workmanship. The warranty does not cover damage
to the product caused by abuse or improper use.
Determination of whether a product failure is the result
of a manufacturing defect or improper use by the
customer shall be made solely by PASCO scientific.
Responsibility for the return of equipment for warranty
repair belongs to the customer. Equipment must be
properly packed to prevent damage and shipped
postage or freight prepaid. (Damage caused by im-
proper packing of the equipment for return shipment
will not be covered by the warranty.) Shipping costs
for returning the equipment after repair will be paid by
PASCOscientific.
Copyright,Warranty,andEquipmentReturn
Please—Feel free to duplicate this manual
subject to the copyright restrictions below.
ii
Equipment Return
Should the product have to be returned to PASCO
scientific for any reason, notify PASCO scientific by
letter, phone, or fax BEFORE returning the product.
Upon notification, the return authorization and ship-
ping instructions will be promptly issued.
ä NOTE: NO EQUIPMENT WILL BE
ACCEPTED FOR RETURN WITHOUT AN
AUTHORIZATIONFROMPASCO.
When returning equipment for repair, the units must be
packed properly. Carriers will not accept responsibility
for damage caused by improper packing. To be certain
the unit will not be damaged in shipment, observe the
followingrules:
➀The packing carton must be strong enough for the
item shipped.
➁Make certain there are at least two inches of pack-
ing material between any point on the apparatus and
the inside walls of the carton.
➂Make certain that the packing material cannot shift
in the box or become compressed, allowing the
instrument come in contact with the packing carton.
Address: PASCOscientific
10101 Foothills Blvd.
Roseville, CA 95747-7100
Phone: [phone]
FAX: [phone]
email: [email protected]
web: www.pasco.com

012-03175E
1
The Model ES-9054B Electrometer is an infinite
impedance (1014 ý) voltmeter that can be used for
direct measurements of voltage, and indirect measure-
ments of current and charge. Because of its high
impedance, it is especially suited for measuring charge
in electrostatic experiments. It has a sensitivity nearly
1,000 times that of a standard, gold-leaf electroscope,
it has a center-zero meter that directly indicates charge
polarity, and it measures charges as low as 10-11
coulombs.
With these features, you’ll find that your electrostatics
demonstrations and labs are easier to perform and, with
quantitative data, are more informative as well.
The electrometer is battery powered by two 9 volt
batteries, and comes complete with the batteries and a
shielded test lead. Instructions for inserting the
batteries are at the end of this manual.
Introduction
The controls on the front panel of the electrometer are
explained in Figure 1. Whether you’re using the
electrometer to measure voltage, current, or charge, the
following procedure should be followed each time you
turn on the electrometer. More information on making
accurate measurements is given in the sections that
follow.
Operation
ä IMPORTANT:
①Never use the Electrometer for measuring
potentials in excess of 100 volts.
②Never connect the electrometer to an electro-
static generator such as a Van de Graff generator
or a Wimshurst machine.
③Never touch the input leads until you have
grounded yourself to an earth ground. A person
walking across a rug on a cool, dry day can easily
pick up a potential of several thousand volts.

012-03175E
2
charge or voltage. Set the FUNCTION switch to the
desired voltage range. The range setting refers to the
voltage input required to produce a full-scale meter
deflection (e.g., a setting of 30 means that a full scale
meter deflection indicates a voltage of 30 volts).
scientific
OUTPUT GND INPUT
Model ES-9054B ELECTROMETER
PUSH
TO
ZERO
POWER
OFF ON
FUNCTION
3
10
30
100
B1 B2
ZERO ADJUST
D
C
V
O
L
T
S
ZERO
LOCK
Mechanical zero adjust screw
(adjust with power off) Select voltage range
(3, 10, 30, or 100
volts full scale) or
test batteries
(B1 and B2)
0-3.6 volts for driving
a projection meter
Setup
①Before turning on the electrometer, check that the
meter reads zero. If not, turn the Mechanical Zero
Adjust screw, located just below the meter face, un-
til it does.
②Slide the POWER switch to the ON position.
③Check the batteries:
a. Turn the FUNCTION switch to B1. The meter
pointer should read to the left of the B1 line at
the bottom of the meter face. If the pointer falls
within the area labeled B1, see the battery re-
placement section at the end of this manual.
b. Turn the FUNCTION switch to B2. The meter
pointer should read to the right of the B2 line at
the bottom of the meter face. If the pointer falls
within the area labeled B2, see the battery re-
placement section at the end of this manual.
④Zero the meter:
a. Turn the FUNCTION switch to 3.
b. Turn the Zero Switch to the ZERO LOCK set-
ting.
c. Adjust the ZERO ADJUST knob so the meter
reads zero volts.
⑤Turn the Zero Switch to the PUSH TO ZERO set-
ting.
⑥Connect the test lead to the INPUT connector of the
electrometer.
⑦Connect the GND post of the electrometer to an
earth ground.
You’re now ready to use the electrometer to measure
ä Important Points for General Operation:
①Between measurements, always press the Zero
Switch to discharge all current from the electrom-
eter. (The Zero Switch must be in the PUSH TO
ZERO setting.) Shorting the test leads together is
insufficient. There may still be stray charges
within the electrometer circuitry.
②When adjusting the zero point of the electrom-
eter, always turn the Zero Switch to the ZERO
LOCK position.
③For good results, it is essential that the elec-
trometer be connected to an earth ground (a water
pipe or the ground wire from a 120 VAC socket).
Only an earth ground provides a sufficient drain
for excess charges that may build up during an
experiment. It is also helpful if the experimenter is
grounded. Just touch one hand to a good earth
ground while, or just before, making measurements.
Figure 1 Front Panel Controls
Zero Switch: In PUSH TO ZERO
setting, pushing knob will
discharge the electrometer
Zero meter (zero
switch should be in
ZERO LOCK position)
Connect test lead here
Connect to earth ground

012-03175E
3
Measuring Charge
Charge measurement with the electrometer is indirect,
but simple. It is based on the relationship Q = CV,
where
Q and V are the charge and voltage across a capacitor
and C is the capacitance. The electrometer can be
thought of as an infinite impedance voltmeter in
parallel with a capacitor, as shown in Figure 2. The
capacitor represents the internal capacitance of the
electrometer, plus the capacitance of the leads.
When a charge is placed across the Electrometer leads,
a voltage V will read on the meter. If the value C is
known, the value of the charge can be calculated as
Q = CV. However, when you touch the Electrometer
leads to another object to test a charge, the capacitance
may change. If the object adds significant capacitance,
the situation becomes as shown in Figure 3. The new
capacitance (C + Cext) must be determined to accurately
calculate the charge from the measured voltage.
Measuring Charge by Induction
Under most conditions, the best way to measure charge
is by induction, using a proof plane and a Faraday ice
pail such as those included with PASCO’s Demonstra-
tion Electrostatics System. The proof plane is simply a
small conductive disk on an insulating handle. You
can make your own ice pail by mounting a conductive
cylinder on an insulating support, and placing a larger
conductive cylinder around it as a shield. Connect the
test lead of the electrometer probe to the inside cylin-
der, and connect the ground lead to the outside cylinder
(see Figure 4).
Volt-
meter V–Q
QC
Internal Capacitance of
Electrometer
(30-35 pf without Test
Probe; approximately
150 pf with Test Probe)
Q = CV
V
Q
–Q
Q'
–Q'Cext
C
Volt-
meter
Capacitance of object
connected to the
Electrometer
Figure 3 Change in Capacitance Due to
Charged Object
Q + Q' = (C + Cext) V
Figure 4 Using a Faraday Ice Pail
To sample the charge distribution on a charged object,
simply touch it with the proof plane, then place the
proof plane inside the inner cylinder of the ice pail,
without touching the cylinder. A charge is induced on
the inside cylinder that is equal but opposite to that on
the proof plane. You can now read the voltage on the
electrometer. By always using the proof plane and the
ice pail, the capacitance will be the same for all your
measurements and the charge on the proof plane will
always be proportional to the voltage reading of the
electrometer. However, in experiments for which you
want to know the absolute charge on the proof plane,
you need to know the total capacitance of the electrom-
eter, plus the test probe, plus the ice pail with the proof
plane inside it. Fortunately, this is easily measured, as
described below. Once you know the capacitance,
you can calculate the absolute charge for any measure-
ment as Q = CV.
Figure 2 Ideal Schematic of the Electrometer
Test lead
Electrometer
Ground lead
Faraday ice pail
Proof Plane

012-03175E
4
To measure the total capacitance:
①Turn on the Electrometer and zero the meter. Clip
the test lead of the probe to the inside cylinder of
your ice pail and the ground lead to the outside cyl-
inder (see Figure 4).
②Use a DC power supply or a statically charged ob-
ject to charge your proof plane.
③Place the proof plane inside the inner cylinder of the
ice pail and adjust the FUNCTION switch to get a
meter reading near full scale. (For convenience, you
may want to touch the proof plane to the inside of
the ice pail and then remove the proof plane. The
effect on the voltage reading should be negligible.)
Record the voltage as Ve. Do not discharge the
Electrometer.
④Take a capacitor of known capacitance, Ck. Ground
the leads of the capacitor to be sure it is fully dis-
charged, then connect the capacitor between the in-
ner and outer cylinder of the ice pail. With the
proof plane still inside the ice pail, record the meter
reading as Vk.
⑤The capacitance of the Electrometer, Ce, can now be
calculated as: Ce = CkVk/(Ve-Vk).
ä EXPLANATION: This measurement is
shown schematically in Figure 3. First the
Electometer is charged with an unknown charge
Q, that must satisfy the equation Q = CeVe, where
Ceis the total capacitance of the system and Veis
the Electrometer reading. Then the second
capacitor is connected in parallel with the capaci-
tance of the Electrometer. The total capacitance
is now Ce+ Ck. The charge Q has not changed,
but now satisfies the equation Q =
(Ce+ Ck)Vk, where Vkis the new Electrometer
reading. Combining the two equations gives,
CeVe= (Ce+ Ck)Vk, or Ce= CkVk/(Ve -Vk).
If you want to use the Electrometer with a different set
of test leads, or a different ice pail, or even a different
proof plane, the capacitance may be different, and you
will need to repeat the above procedure to measure the
new capacitance.
ä NOTE: The capacitance of the Electrometer
is 30-35 pf. With the test probe, the total capaci-
tance is approximately 150 pf. For best results,
measure the total capacitance.
Measuring Charge by Contact
Charges can also be measured by contact. You’ll find, for
example, that if you touch the charged proof plane to the
inside cylinder of the ice pail, the Electrometer reading will
generally remain relatively unchanged. This is because the
total capacitance is only negligibly affected by the proof
plane. This may not always be the case, however.
In general, contact measurements can be carried out in
much the same way as inductive measurements using
the ice pail. Touch the object with the test probe,
record the voltage V, and use Q = CV to calculate the
charge. However, if you suspect the object for which
you are measuring the charge appreciably affects the
total capacitance of the system, you will need to
remeasure the capacitance as described above.
Measuring Voltage
Voltage can be measured as with any voltmeter.
Connect the leads to the circuit, set the range (3, 10,
30, or 100 volts full scale), and read the voltage on the
meter.
Measuring Current
The Electrometer can be used for indirect current
measurements in many situations, though it is no
substitute for a good ammeter. Connect the Electrom-
eter leads across a known resistance in the circuit and
measure the voltage. Use Ohm’s law (Voltage =
Current x Resistance) to determine the current. The
effect of the Electrometer on the circuit will be negli-
gible in most circuits due to its exceedingly high input
impedance. However, the voltage drop across the
resistor must be within the voltage range of the Elec-
trometer.
If it is not convenient to hook the Electrometer across a
known resistance in the circuit, a precision resistor can
be connected between the input leads of the Electrom-
eter. The circuit can then be broken, as for connection
to a standard ammeter, and connected in series with the
precision resistor. Again, measure the voltage across
this resistor and calculate the current. (The problem
with this technique is that the resistance must be high
enough so the voltage drop is easily measured, but low
enough so it doesn't significantly affect the current
through the circuit.)
Using a Projection Meter
The OUTPUT connectors on the ES-9054B Electrom-
eter provide an output signal for driving a projection
meter, oscilloscope, or other monitoring device. The
output is proportional to meter deflection (within 10%)
with a
±3.6 VDC output corresponding to a full scale deflec-
tion. (The OUTPUT voltage depends only on meter
deflection. It is independent of the range setting of the
FUNCTION switch.)

012-03175E
5
ä CAUTION: Whenever you open your
Electrometer, do not touch any of the compo-
nents on the printed circuit board other than the
battery holders or the trim potentiometers. The
printed circuit contains the high impedance
MOS-FET input which can be damaged just by
touching the wrong lead.
Battery Installation
To install or replace the batteries, remove the four
screws that fasten the front panel to the case, then
gently lift the front panel out of the case. Install the
batteries as shown in Figure 5. When removing and
installing the batteries, be careful not to bend the
battery clips or pull the battery wires out of the circuit
board. Place the new batteries in the clips with the
positive terminal closest to the printed circuit
board.Before replacing the front panel, test that the
batteries are good and the connections are secure by
flipping the FUNCTION switch first to B1 and then to
B2. The meter pointer should be deflected out beyond
the areas labeled B1 and B2, respectively, at the
bottom of the meter face. Replace the front panel.
PASCO’s Model ES-9065 Projection Meter can be
used with an overhead projector to display the Elec-
trometer readings for the whole class. The Projection
Meter connects directly to the OUTPUT jacks, red to
red and black to black.
To calibrate the Projection Meter:
①Set the FUNCTION switch to 3, and the Zero
Switch to ZERO LOCK.
②Turn the ZERO ADJUST knob until the meter on
the Electrometer reads as close to full scale as
possible (either postive or negative).
③Adjust the CALIBRATE knob on the Projection
Meter so that the Projection Meter reads the same
as the Electrometer.
④Turn the ZERO ADJUST knob until the Electrom-
eter and the Projection Meter read zero.
Checking Out Your Electrometer
①Follow the setup instructions on pages 2-3 of this
manual to check the batteries and zero the Elec-
trometer. If the batteries are low, see “Battery In-
stallation.” If the meter cannot be zeroed, see
“MOS-FET Replacement.”
②Calibration Test: Set the FUNCTION switch to
30 and connect the input to an accurate 30 VDC
source. If the meter does not read 30 volts ±5%,
see “Calibration.”
③Input Impedance Test: Set the FUNCTION
switch to 30 and connect the input to a 30 VDC
source. Disconnect the input cable at the front
panel input connector. Record the meter reading
and the time. If the input impedance is sufficient, it
will take 15 minutes or longer for the meter reading
to decrease to 30% of its initial value. If the input
impedance is low, see “Repairs.”
④Zero Drift Test: With the meter zeroed, short the
leads of the input cable together. Turn the Zero
Switch to PUSH TO ZERO and depress the knob,
then release it. The meter should read zero volts
and should drift by no more than 75 mV/minute.
At any time, depressing the Zero Switch should
bring the meter immediately back to zero. If the
zero drift is excessive, see “Repairs.”
ä IMPORTANT: A zero drift test is best
performed after the Electometer has been left
unused with the Zero Switch in the ZERO LOCK
position for at least four hours. During use with
high voltages, or during battery replacement or
other maintenance, charges may be produced on
the insulators of the input circuit. The bleeding
off of these charges may appear as excessive zero
drift.
Battery 1 (B1) Battery 2 (B2)
Calibration
Potentiometer
Zero Calibration
Potentiometer
MOS-FET
Figure 5 Inside the Electrometer
Maintenance

012-03175E
6
④The replacement MOS-FET will probably come in
an anti-static bag or may be wrapped in aluminum
foil. The leads will be protected by a thin ring or
spring that is wound around the leads near where
they protrude from the base of the transistor. Gently
remove the MOS-FET from the bag or foil, but do
not remove the thin wire ring that is around the
leads. Leave this wire ring in place until after the
MOS-FET is seated in the socket.
⑤The MOS-FET has a small metal tab protruding
from one side (see Figure 6). The lead directly be-
low the tab (as seen from the top side of the transis-
tor) is lead number 8. Count back to lead number
5, as shown, and gently bend the lead up.
⑥Insert the leads of the MOS-FET, except for lead 5,
into the socket so that the metal tab lines up with
the notch on the side of the socket as shown in the
figure.
⑦Insert lead number 5 into the socket that is con-
nected to the adjacent binding post. This may be
done by
inserting the lead through the slot in the end of the
socket, and then bending the end of the lead back
and crimping it tightly. Now gently pull off the thin
ring of wire that is wound around the leads. This
may require thin nose pliers or "tweezers".
⑧Replace the cover.
Repair
Should your Electrometer have problems that are not
covered in the preceding sections, we strongly suggest
you return it to PASCO scientific for repair.
Calibration
①Remove the four screws that fasten the front panel
to the case, then gently lift the front panel out of the
case.
②Turn the POWER switch to ON.
③Set the FUNCTION switch to 3.
④Flip the Zero Switch to ZERO LOCK. With the
¯zero adjust knob midway between its extreme cw
and ccw positions, adjust the Zero Calibration Po-
tentiometer to zero the meter.
⑤Set the Function Switch to 30, zero the meter using
the zero adjust knob on the front panel, then con-
nect the INPUT of the Electrometer to a known, ac-
curate 30 VDC source.
⑥Flip the Zero Switch to the PUSH TO ZERO set-
ting.
⑦Adjust the Calibration Potentiometer (see Figure 5)
until the meter reads 30 volts.
⑧Press the Zero Switch, then release it. The meter
should still read 30 volts. If it doesn’t, readjust the
Calibration Potentiometer until it does.
MOS-FET Replacement
If the meter can’t be zeroed using the ZERO ADJUST
knob with the Zero Switch set to ZERO LOCK, the
MOS-FET has probably failed. (MOS-FET is an
acronym for Metal Oxide Semiconductor-Field Effect
Transistor). You can order a replacement from
PASCO scientific (Part # 422-001) . When ordering a
replacement part, be sure to include the model number
of the Electrometer.
To replace the MOS-FET:
①Turn the Electrometer off.
②Remove the four corner screws that fasten the front
panel to the case, and gently lift out the front panel.
③Gently pull the MOS-FET out of its socket (see Fig-
ure 5). Avoid yanking or twisting it, as this may
damage the transistor socket.
1
3
2
4
56
7
8
MOS-FET
Align pin 8, the pin
directly below the
tab, with the notch
in the socket, as
shown.
Insert pin 5 into
this socket
Figure 6 MOS-FET Installation

012-03175E
7
SCHEMATIC
Model ES-9054B Electrometer
(Drawing #956-02859)

012-03175E
8
Reference Description PASCO Part #
R1,2,5,13, Resistor, 10 ký, 1/4 W, 5% 113-103
20,21
R3 Resistor, 1 ký, 1/4 W, 5% 113-102
R4 Resistor, 13 ký, 1/4 W, 5%, C.C. 113-133
R6,24 Resistor, 470 ý, 1/4 W, 5% 113-471
R7 Potentiometer, 10 ký, 1/4 W, 30% 140-006
R8 Resistor, 330 ý, 1/4 W, 5% 113-331
R9 Trimpot, 500 ý 142-031
R10,11,19 Resistor, 3.01 ký, 1/8 W, 1%, MF 124-007
R12 Resistor, 470 ký, 1/4 W, 5% 113-474
R14 Resistor, 301 ý, 1/8 W, 1% 124-004
R15 Resistor, 698 ý, 1/8 W, 1%, MF 124-005
R16 Resistor, 2 ký, 1/8 W, 1%, MF 124-006
R17 Resistor, 6.98 ký, 6.81 ký, 1/8 W, 1% 124-008
R18 Potentiometer, 5 ký, 10% 142-018
R22 Resistor, 100 ý, 1/4 W, 5% 113-101
R23 Resistor, 100 Mý, 1/2 W, 20% 150-007
C1,3 Capacitor, 1.0 µf, 10%, 35 V, Axial 220-004
C2,5 Capacitor, 0.1 µf, 25 V, Monolithic 210-018
C4 Capacitor, 100 pf 210-014
C6 Capacitor, 0.001µf, 5%, 600 V 216-013
C7 Capacitor, 24 pf, 5%, 600 V 216-003
Q1 Transitor—2N3906 420-003
Q2 Transistor—MOS-FET 3N190 422-001
U1 IC—TL431 Voltage Regulator 430-083
U2 IC—LM324N 430-027
S1 Switch—Slide, 2 Pole, 2 Position 512-007
S2 Switch—2 Pole, 6 Position, Rotary 510-019
M1 Meter 525-00682
Parts List

012-03175E Electrometer
TechnicalSupport
Feedback
If you have any comments about the product or manual,
please let us know. If you have any suggestions on
alternate experiments or find a problem in the manual,
please tell us. PASCO appreciates any customer
feedback. Your input helps us evaluate and improve our
product.
To Reach PASCO
For technical support, call us at 1-800-772-8700
(toll-free within the U.S.) or [phone].
fax: [phone]
e-mail: [email protected]
web: www.pasco.com
Contacting Technical Support
Before you call the PASCO Technical Support staff, it
would be helpful to prepare the following information:
➤If your problem is with the PASCO apparatus, note:
Title and model number (usually listed on the
label);
Approximate age of apparatus;
A detailed description of the problem/sequence of
events (in case you can’t call PASCO right away,
you won’t lose valuable data);
If possible, have the apparatus within reach when
calling to facilitate description of individual parts.
➤If your problem relates to the instruction manual,
note:
Part number and revision (listed by month and
year on the front cover);
Have the manual at hand to discuss your
questions.