Monroe Electronics 284 User manual

Operator’s Manual
Model 284
NanoCoulomb Meter
P/N 0340117
284-1/100
08012017
100 Housel Ave  PO Box 535  Lyndonville NY 14098
585-765-2254  fax: [phone] monroe-electronics.com

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% OF READING, + Zero offset, +/- 1 lsd.
Output: 0 to ±2 volt analog, 1k
Drift: 0.1pC/sec. Typical
Battery: 9 volt Eveready #216 or equivalent NEDA #1604.
Battery life over 400 hours.
Dimensions: 6” x 3½” x 21/8” (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)— 25/8” dia. x 2¾” deep
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 3-foot mating cable
to connect to Model 284 instrument. Can be used to measure powders and liquids as
well as solid objects.
Point contact probe:
Various—contact factory
Accessories Included: Banana Patch Cable with Alligator Clip
Operator’s Manual
9V Battery

Section 2
GENERAL INFORMATION
The Monroe Electronics Model 284 Nanocoulomb Meter is a convenient battery powered
portable instrument for direct measurement of charge in the range between 1 picocoulomb (limit
of resolution) and 2 microcoulombs (maximum displayable value). The standard instrument
configuration provides two ranges—±19.99nC and ±199.9nC—with one-decade extension in
either direction available as a factory option at time of order or as an aftermarket upgrade.
The NanoCoulomb Meter charge amplifier consists of an I.C. electrometer amplifier with a high
quality capacitor connected in the negative feedback position. The input terminal (center pin of
a BNC connector) feeds 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 transferred to the integrating capacitor. Since Q=CV, the
output voltage of the charge amplifier is directly proportional to the charge injected in the input,
that is, for a 0.1F integrating capacitor, 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 readings.
The NanoCoulomb meter is zeroed by a low leakage momentary contact switch, which
discharges the integrator. A built-in reference quality voltage splitter 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 source 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 the electrometer. These are available in two standard sizes or may be custom designed to
order.
The point contact probe is held in a manner similar to which one would hold a pen or pencil and
is used to make charge measurements by direct contact with small objects or small areas of
objects such as individual pins on IC’s.
Any input device used must have low leakage (>1011) and provide an electrical reference
(usually earth ground).

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 right 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 outside electric fields may be affecting readings.
One can measure both “mobile” and “immobile” charge in objects to be tested. To do this,
follow the above procedure. After 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
“mobile” charge on the object being tested.
Since “total” charge = “mobile” charge + “immobile” charge, we can calculate the “immobile”
charge by subtracting the “mobile” charge from the “total” charge.

Section 4
ZERO ADJUST
Disconnect all input connections from the Model 284.
Turn Model 284 on and set on most sensitive range.
Push and release “ZERO” button.
Adjust zero. The zero potentiometer is located through the small hole ½” (1.3 cm) to the right of
the zero button.
CALIBRATION CHECK
The purpose of this section is to provide the operator 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 (0.01F) (Mallory SX-110 or equivalent).
With the capacitor 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 the capacitor value (±2%) should appear on the Digital Panel Meter (DPM) set
to the 20-nCoulomb range.
Charging the calibration capacitor to 10.00 volts and then discharging it into the input should
produce a DPM reading of ten times the capacitor value (±2%) on the 200-nCoulomb range.
It is important to handle the calibration capacitor very carefully. Do not hold the capacitor by its
body or discharge it by touching both leads with the fingers. Hold the capacitor by one lead only.
Use a clip-lead connected between the GND jack and this lead of the capacitor to maneuver the
other 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 calibration.

WARRANTY
Monroe Electronics, Inc., warrants to the Owners, this instrument to be free from defects in material and workmanship
for a period of two years after shipment from the factory. This warranty is applicable to the original purchaser only.
Liability under this warranty is limited to service, adjustment or replacement of defective 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 sub-assemblies subjected to abuse, abnormal operating conditions, or
unauthorized repair or modification.
Since Monroe Electronics, Inc. has no control over conditions 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 implied warranties of
merchantability 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 warranty, 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 factory repair work. Material being returned to the factory for repair must have a
Return Material Authorization number. To obtain an RMA number, call 585-765-2254 and ask for Customer Service.
Material returned to the factory for warranty repair should be accompanied by a copy of a dated invoice or bill of sale,
which serves as a proof of purchase for the material. Serial numbers, date codes and tamper proof stickers on our
products also serve to determine warranty status. Removal of these labels or tags may result in voiding a product’s
warranty.
Repairs will be returned promptly. Repairs are normally returned to the customer by UPS within 10 to 15 working
days after receipt by Monroe Electronics, Inc. Return (to the customer) 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.
RETURN OF REPAIRED ITEMS:
Factory repairs will be returned to the customer by the customer’s choice of FedEx, DHL or UPS. Warranty repairs
will be returned via UPS ground. The customer may request accelerated shipping via the previous mentioned
carriers for both warranty and non-warranty repairs. NOTE: Accelerated transportation expenses for all 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 factory for repair that has been modified will not be tested unless the nature and purpose of
the modification is understood by us and does not render the equipment untestable at our repair facility. We will
reserve the right to deny service to any modified equipment returned to the factory for repair regardless of the
warranty status of the equipment.