m
Operators’ Manual
Monroe Electronics, Inc.
Model 284
NanoCoulomb Meter
P/N 0340117
284-1/100
Rev A
100 Housel Ave PO Box 535 Lyndonv il le NY 14098 1-800-821-6001 585-765-2254 fax: 585-765-9330 monroe-electronics.co
Section 1
SPECIFICATIONS:
Display: ½” x 3½ digit LCD
Standard Ranges:
Range: Resolution:
200nC 0.1nC
20nC 0.01nC
Optional Ranges Available:
Range: Resolution:
2000nC 1.0nC
2.0nC 0.001nC
Accuracy: 2%
Output: 0 to ±2 volt analog, 1kΩ
Drift: 0.1pC/sec. Typical
Battery: 9 volt Eveready #216 or equivalent NEDA #1604.
Battery life over 400 hours.
1
Dimensions: 6” x 3½” x 2
/8” (150mm x 90mm x 54mm)
Weight: 8½ oz. (0.24 kg) with battery
Compatible accessory probes:
Faraday Cup, Model 284/22A:
Outer dimensions (nominal)—
3½” dia. x 5¾” tall
Inner dimensions (nominal)—
5
/8” dia. x 2¾” deep
2
Faraday Cup, Model 284/22B:
Outer dimensions (nominal)—
8” dia. x 10” tall
Inner dimensions (nominal)—
6” dia. x 6¾” deep
Faraday Cups are equipped with BNC connectors and furnished with 3foot mating cable to connect t o Model 284 instrum ent . Can be used to
measure powders and liquids as well as solid objects.
Point contact probe:
Various—contact factory
Page 1 284.CBSM-12/98-RCA
Section 2
GENERAL INFORMATION
The Monroe Electronics Model 284 Nanocoulomb Meter is a convenient battery
powered portable instrument for direct measurement of charge in t he r ange
between 1 picocoulomb (limit of resolution) and 2 micr ocoulom bs ( maximum
displayable value). The standard instrument conf iguration provides two ranges—
±19.99nC and ±199.9nC—with one-decade extension in either direction available
as a factory option at time of or der or as an aftermark et upgrade.
The NanoCoulomb Meter charge amplifier consists of an I.C. electrometer
amplifier with a high quality capacitor connect ed in the negative feedback
position. The input terminal (center pin of a BNC connector) f eeds the inverting
input of the amplifier through a current limiting resistor. This inverting input is at
zero volts or virtual ground so all charge that is induced or directly deposited at
the input terminal is transf er red to the integrating capacit or. Since Q=CV, the
output voltage of the charge amplifier is directly proportional t o t he charge
injected in the input, that is, for a 0.1µF integrating capacit or , a +100
nanocoulomb input equals −1.0 volt at the output . The input being at virtual
ground reduces leakages and polarization of insulators, thus minimizing these
effects on the reading s.
The NanoCoulomb meter is zeroed by a low leakage momentar y contact switch,
which discharges the integrator. A built-in reference quality voltag e split ter
corrects for all offsets.
The electrometer is followed by a scaled-gain inverter , which is used to correct
the gain error caused by variations in capacitors and the inversion of the input
amplifier and to drive the 3½ digit Liquid Crystal Display (LCD) and the analog
output circuit.
The readout is thus always expressed directly in nanocoulombs with the decimal
point properly placed and the output is always 2 volts for full scale, regardless of
range.
In order to be fully functional, the Model 284 requires some sort of input sour ce
device. Two types of input devices are readily available from Monroe Electronics
as accessories to the Model 284—Faraday cups and contact probes.
The Faraday cup consists of two concentric cans with expanded polyethylene as
an insulator between them. The outer can is at ground potential and the inner
can is the sensing electrode for t he elect r ometer. These are available in two
standard sizes or may be custom designed to order.
The point contact probe is held in a manner similar t o which one would hold a
pen or pencil and is used to make charge measurem ent s by direct cont act with
small objects or small areas of objects such as individual pins on IC’s.
11
Any input device used must have low leakage (>10
Ω) and provide an electrical
reference (usually earth ground) .
Page 2 284.CBSM-12/98-RCA
Section 3
OPERATION
The Monroe Electronics Model 284 Nanocoulomb Meter has been designed for
extreme ease of operation.
1. Connect Faraday cup to Model 284.
2. Switch power on.
3. Set to least sensitive range (decimal point furthest to the rig ht for your
instrument).
4. Zero the instrument.
5. Place charged object in cup and take reading.
The Faraday cup comes with a cover, which can be used when zeroing or when
taking readings in areas where one suspects that out side electric fields may be
affecting readings.
One can measure both “mobile” and “immobile” char ge in objects to be tested.
To do this, follow the above procedure. Af ter step 5, note the reading (this
reading is the “total” charge reading). Then remove the object being tested by
dumping it out of the cup or by lifting it out with a set of wooden tongs. The
reading that is now being displayed in the meter is the “ m obile” char ge on the
object being tested.
Since “total” charge = “mobile” char ge + “immobile” charge, we can calculate the
“immobile” charge by subtracting the “mobile” charge fr om the “total” charge.
Page 3 284.CBSM-12/98-RCA
Section 4
CALIBRATION CHECK
The purpose of this section is to provide the oper at or of the Monroe Electronics
Model 284 Nanocoulomb Meter with a means of verifying that overall calibration
of the instrument is within the specified limits (±2%).
Method 1:
Procure a calibration capacitor. It should be a polystyrene or polypropylene
capacitor with a precisely known value of approximately 10nF (0.01µF) (Mallory
SX-110 or equivalent).
With the capacit or charged to exactly 1.00 volt and then discharged directly into
the input terminal (BNC connector) or between the inner and outer parts of the
Faraday cup, a meter reading equal to t he capacitor value (±2%) should appear
on the Digital Panel Meter (DPM) set to the 20-nCoulomb range.
Charging the calibration capacitor t o 10.00 volts and then discharging it into the
input should produce a DPM reading of ten times the capacit or value (± 2%) on
the 200-nCoulomb range.
It is important to handle the calibr ation capacitor very carefully. Do not
hold the
capacitor by its body or discharge it by touching both leads with the f ingers. Hold
the capacitor by one lead only
. Use a clip-lead connected between the GND jack
and this lead of the capacitor to maneuver t he ot her lead of the capacitor
between the “hot” side of the charging source and the input terminal.
Method 2:
Use a secondary standard charge source such as a Keithley Model 263
Calibrator/Source, following manufacturer’s instructions.
Incorrect DPM readings indicate a need for calibr ation.
Page 4 284.CBSM-12/98-RCA
WARRANTY
Monroe Electronics, Inc., warrants to the Owners , this instrument to be fr ee from defects in material and
workmanship f or a period of two years after shipm ent from the factor y. This warranty is applicable to the
original purchaser only.
Liability under this warranty is limited to service, adjus tment or replac ement of def ective parts (other than
tubes, fuses or batteries) on any instrument or sub-assembly returned to the factory for this purpose,
transportation prepaid.
This warranty does not apply to instruments or s ub-assemblies subjected to abuse, abnorm al operating
conditions, or unauthorized repair or modification.
Since Monroe Electronics, Inc. has no control over c onditions of use, no warranty is made or implied as to
the suitability of our product for the customer’s intended use.
THIS WARRANTY SET FORTH IN THIS ARTICLE IS EXCLUSIVE AND IN LIEU OF ALL OTHER
WARRANTIES AND REPRESENTATIONS, EXPRESS, IMPLIED OR STATUTORY INCLUDING BUT
NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. Except for
obligations expressly undertaken by Monroe Electronics, in this Warranty, Owner hereby waives and
releases all rights, claims and remedies with respect to any and all guarantees, express, implied, or
statutory (including without limitation, the im plied warranties of m erchantability and fitness), and including
but without being limited to any obligation of Monroe Electronics with respect to incidental or
consequential damages, or damages for loss of use. No agreement or understanding varying or
extending the warranty will be binding upon Monroe Electronics unless in writing signed by a duly
authorized representative of Monroe Electronics.
In the event of a breach of the foregoing warr anty, the liability of Monroe Electronics shall be limited to
repairing or replacing the non-conforming goods and/or defective work, and in accordance with the
foregoing, Monroe Electronics shall not be liable for any other damages, either direct or consequential.
RETURN POLICIES AND PROCEDURES
FACTORY REPAIR:
Return authorization is required for factor y repair work. Material being returned to the factory for repair
must have a Return Material Authorization number. To obtain an RMA num ber, call 716-765-2254 and
ask for Customer Service.
Material returned to the factory for warranty repair must be acc ompanied by a copy of a dated invoice or
bill of sale, which serves as a proof of purchase for the material.
Repairs will be returned promptly. Repairs are normally returned to the customer by UPS within ten
working days after receipt by Monroe Electronics, Inc. Retur n (to the custom er) UPS charges will be paid
by Monroe Electronics on warranty work. Return (to the customer) UPS charges will be prepaid and
added to invoice for out-of-warranty repair work.
EXPEDITED FACTORY REPAIR:
All material returned to the fac tory by air or by an overnight service will be expedited. Expedited factory
repairs will be returned to the custom er by the same mode of transportation by which the material was
returned to the factory for repair (i.e., material returned to the factory by an overnight service will be
returned to the customer by an overnight service).
NOTE: Return (to the customer ) transportation expenses for expedited factory repairs will always be at
the expense of the customer despite the warranty status of the equipment.
FACTORY REPAIRS TO MODIFIED EQUIPMENT:
Material returned to the f actory for repair that has been modified will be not tested unless the natur e and
purpose of the modification is understood by us and does not render the equipment untestable at our
repair facility. W e will reser ve the right to deny service to any modified equipment returned to the f actory
for repair regardless of the warranty status of the equipment.
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