Monroe Electronics 268A User Manual

Operator’s Manual

Charged Plate Analyzer

Model 268A-1

100 Housel Ave ⏐ PO Box 535 Lyndonville NY 14098 1-800-821-6001⏐ 585-765-2254 ⏐ fax: [phone] ⏐monroe-electronics.com

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 585­765-2254 and ask for Customer Service.
Material returned to the factory for warranty repair must be accompanied 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. 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.

EXPEDITED FACTORY REPAIR:

All material returned to the factory by air or by an overnight service will be expedited. Expedited
factory repairs will be returned to the customer 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 factory for repair that has been modified will be not 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.

TABLE OF CONTENTS

Warranty

Section 1 ...................Specifications

Section 2 ..........General Information

Section 3 ..........................Operation

Section 4 .....................Maintenance

APPENDIX I....................................

Variable Timer Trip Point Option

APPENDIX II...................................

Application Note APNE-0017
Plate Self Decay of Charged Plate Monitors

Copyright© 1998

Monroe Electronics, Inc.

Printed in USA

P/N 0340097

Rev: 071006

Section 1

SPECIFICATIONS

CHARGED PLATE/PROBE ASSEMBLY:

 Designed to EOS/ESD Association standard
 Standard tripod mount
 Dimensions: 6” X 6”
 Capacitance: Total discharge test circuit with plate 20 picofarads, ±2

picofarads

 Plate self-discharge: Less than 10% of set voltage within 5 minutes below

50% RH at 25°C

POWER SUPPLY:

±7500 volts maximum output; ±1000 volts/±5000 volts charging of isolated
plate available, adjustable from <±1000 to >±5000 volts

ELECTROSTATIC FIELDMETER:

RANGE: 0 to ±7500 volts; 0 to ±2000 volts—switch selectable
ACCURACY: Better than 2%
DRIFT: Less than 0.4% per hour non-cumulative after 10 minutes

stabilization, typical
SPEED OF RESPONSE: Less than 100ms for 10% to 90% of full scale either

range
OUTPUT: Divide input by 1000, impedance 100Ω

TIMER:

Full scale 999.9 sec. (>16 min.), 0.1 sec. Resolution

POWER REQUIREMENTS:

117 or 220 volts ±10% (factory preset), 50/60 Hz, 5 watts

SIZE AND WEIGHT:

Height 6¾”, Width 6¾”, Depth 9½”; 5.5 lbs.
(17 x 17 x 24 cm, 2.3kg)

Section 2

GENERAL INFORMATION

The Charged Plate Analyzer Model 268A separates into two components
connected by a ten-foot cable. The top part with the plate attached contains the
fieldmeter portion of the instrument and may be placed at the measurement site.
The bottom part with the controls and indicators may be placed in a convenient
operating location remote from the detector. To separate the two components,
release the two over-center latches near the rear of the unit and lift up at the rear
of the top section.

A ¼-20-threaded receptacle is provided inside of the top section for convenient
tripod mounting.

Two foldout legs are provided underneath the bottom of the control unit to
elevate the front of the cabinet to permit easy viewing of the meters.

Switches on the front panel are alternate action push-push type with the
exception of the three used for “plate control”. These are mechanically
interlocked so that only one function can be selected at a time.

Controls are grouped by function.
The three pushbutton switches directly beneath the “PLATE VOLTAGE” meter

relate to meter range and function.
The three switches at the lower center of the panel labeled “PLATE CONTROL”

affect the charge/discharge condition of the plate.
The “HV” control knobs, the “HV ON” indicator and the “POLARITY” pushbutton

switch relate to the polarity and magnitude of the initial charge voltage on the
plate.

The “TIMER LIMIT” switch sets the start/stop voltage limits for the timer.
The “OUTPUT” BNC connector (on the back panel) allows an oscilloscope or

recorder to be connected to the output of the fieldmeter. The signal here is
1/1000th of the actual voltage on the plate—regardless of the settings of the
meter range and function switches.

Two small holes are provided in the plate for the attachment of standard or
miniature banana plugs, useful for measuring induced charge or decay rate on
personnel.

IMPORTANT NOTE

In order to maintain proper operation of the floating plate, it is essential
that the support insulators be kept scrupulously clean. Consider the
following:

 Do not touch or handle the insulators.
 Do not wrap the line cord around the insulators.
 Store the instrument in its protective case when not in use. Store in a clean

dry location.

 Clean the insulators according to the directions given in the MAINTENANCE

section when self-discharge exceeds 10% of the set voltage within 5 minutes
at relative humidity of less than 50%. At high humidity surface leakage
currents increase and air ionizes readily and self-decay time can be expected
to decrease regardless of how clean the insulators are.

The Charged Plate Analyzer Model 268A meets test equipment requirements of
the EOS/ESD Association’s EOS/ESD STANDARD NO. 3.1 “STANDARD FOR
PROTECTION OF ELECTROSTATIC DISCHARGE SUSCEPTIBLE ITEMS:
IONIZATION”.

Monroe Electronics, Inc. does not supply copies of standards.
Copies of the standard are available from:

EOS/ESD Association, Inc.
7902 Turin Rd.
Bldg 3 Suite 2
Rome, NY 13440-2069
Phone [phone]
Fax [phone]
[e-mail]

Section 3

OPERATION

BASIC OPERATION - DISCHARGE MODE:

1. Separate sections and position as necessary. Connect to the proper power
source and press “|” on the power switch to apply instrument power. The
displays will indicate that power is on.

2. Select a polarity. For discussion purposes, we will select positive. Press the
POLARITY pushbutton in to lock.

3. Select a range. We will use 5kV as an example. Release the 5kV/2kV
pushbutton under the PLATE VOLTAGE meter.

4. Select NORMAL mode by releasing the NORM/PK pushbutton (under the
meter).

5. Select TIMER LIMIT. Release the TIMER LIMIT pushbutton to set limits to
5kV and 500 volts. In general, the setting of this function should concur with
the meter range selected.

6. Zero the plate by pressing the ZERO button. This removes all voltage from
the plate. (It connects the plate to ground through a 10k-ohm resistor.)

7. Charge the plate. Press the CHARGE button. The HV light indicates that the
high voltage is on. The PLATE VOLTAGE meter will indicate some voltage.
Adjust the voltage to a minimum of approximately 5kV +3% (5150 volts).

8. Allow the plate to decay. Press the DECAY pushbutton. In the absence of
ions, the plate will decay very, very slowly. In a balanced ion field, the plate
will decay at a more rapid rate.

9. As the plate voltage crosses the +5000 volt level, the timer will start. As the

plate crosses the +500 volt level, the timer will stop and indicate the elapsed
time interval between these two levels. Whenever the plate is recharged, the
timer will be reset for the next test.

BASIC OPERATION - PEAK MODE:

Peak mode is useful for checking balance in pulse ionizing systems. The timer is
not associated with these measurements. The internal high voltage charging
source is not normally used.

The switches used in making peak measurements are the three selector
switches under the PLATE VOLTAGE meter and the ZERO and DECAY
switches.

1. Select a meter range using the 5kV/2kV switch.

2. Zero the plate by depressing the ZERO switch.

3. Select desired peak (+ or –).

4. Select PEAK mode by depressing the NORM/PK switch into the PK position.

5. Allow the plate to “float” by depressing the DECAY button. This ungrounds
the plate. The meter will now indicate the highest peak voltage attained by
the plate in the selected polarity. The
–PK/+PK switch may be shifted to the opposite position to read the highest
peak voltage attained in that polarity.

To balance your ionization system or blower, adjust until both positive and
negative peak readings are the same.

6. Anytime the NORM/PK button is released to the NORM position; the peak
detector is automatically reset.

7. The plate will continue to float until the ZERO button is pressed. Thus, the

ZERO switch and the RESET function of the NORM/PK switch are normally
used in conjunction with each other.

Section 4

MAINTENANCE

GENERAL:

Field maintenance of Model 268A should be limited to cleaning of the insulating
standoffs, cleaning of the case and occasional field-meter zero adjustment.

Further repairs and adjustment require special equipment and are beyond the
scope of this manual.

Factory service is advised.

CLEANING, INSULATORS:

The insulating standoffs (supporting the measuring plate) are specifically
designed to minimize the effects due to contamination of their outer surfaces.
Leakage paths created by the skin oils in fingerprints, tobacco smoke, dust, etc.
will eventually degrade their performance such that the self-decay rate of the
plate will exceed 10% over a five-minute period, indicating the need for cleaning.

IMPORTANT!

DO NOT USE SOAP, DETERGENT OR TAP WATER

TO CLEAN THESE INSULATORS

Clean the exposed surfaces of the insulators with mixture of 70% clean technical
grade isopropyl alcohol and 30% distilled water, using a soft toothbrush. The unit
should be inverted while doing this to minimize the amount of liquid entering the
case.

The insulators should then be allowed to air-dry.

CLEANING, CASE:

General cleaning of the case for aesthetic reasons is best done with a clean lint­free cloth or wiping pad dampened in the alcohol/water solution noted above.

FIELDMETER ZERO:

Airborne contaminants entering the sensitive aperture of the fieldmeter probe
may cause a zero shift, which will affect the accuracy of measurement.

A multi-turn potentiometer is provided on the upper section of the instrument to
adjust fieldmeter zero. Adjust for an indication of zero volts on the 2000 volt
meter range with the ZERO button pressed in.

APPENDIX I

MODEL 268A-1T CHARGED PLATE ANALYZER

WITH VARIABLE TIMER OPTION

VARIABLE TIMER OPTION

The Model 268A-1T Charged Plate Monitor with variable timer stop option has
the same two timer ranges as the standard unit when set in the “FIXED” mode of
operation. In the optional “VARIABLE” timer mode, timing will start at either 5000
volts or 1000 volts as selected by the user. The timer will then stop at a user­selected voltage set on the front panel mounted turns-counting dial from 0 to
1000 volts with 1-volt increments.

This option is available either factory installed at the time of purchase or as a
factory installed aftermarket upgrade to the basic Model 268A-1

VARIABLE TIMER OPTION OPERATING INSTRUCTIONS

1. Power unit on.

2. Select either 5kV or 2kV plate voltage level (measuring range).

3. Make sure NORM/PEAK button is in NORM position (not depressed).

4. Set timer STOP LEVEL (turn pot) to desired plate voltage stop level (0 to
1000 volts).

5. Press VARIABLE on TIMER LIMIT switch.

6. Select 5kV or 1kV timer start level on TIMER LIMIT switch.

7. Select appropriate (+ or –) POLARITY for plate voltage.

8. Press CHARGE button and adjust to voltage above desired start voltage
level.

9. Press DECAY button.

10. Observe PLATE VOLTAGE indicator as it decays. Timer indicator
(SECONDS) will stop when variable trip point is met.

11. For additional tests, repeat steps 8 thru 10.

Note: To return unit to normal operation, switch unit to FIXED on the TIMER
LIMIT switch.

APPENDIX II

Application Note APNE-0017

Plate Self Decay of Charged-Plate Monitors

Introduction

Charged-Plate Monitors (CPM’s) evaluate the ability of air ionizers to neutralize
static charge. A CPM charges an isolated, conductive plate that is charged to a
known level. Then the air ions produced by the ionizer neutralize the charge on
the isolated plate, and the time required to discharge the isolated plate is meas­ured.

In an ideal, traditional CPM, the plate is perfectly isolated from ground and
represents a perfect capacitor. Once the plate is charged to a known level, it
would hold that charge indefinitely. The only cause for the isolated plate to dis­charge would be by impingement of air ions.

In practice, other factors may exist that cause the isolated plate to discharge. In
the absence of air ions, any discharge of the isolated plate is known as plate self
decay or plate isolation.

The Problem

As the isolated plate in a traditional CPM is supported from ground by one or
more insulating supports, a common cause of self decay is leakage through
these insulative supports.

The two major contributors to leakage across these supports are:

• High humidity, and,

• Lack of cleanliness.

Any substance (contamination) that is deposited on the surface of the insulative
supports, such as salts and oils from fingers, and dust, may increase the
conductivity of the support and increase the leakage from the isolated plate to
ground. Moisture in the air can be absorbed into the surface layers of the support
and further increase the surface conductivity of the material. Moisture may also
activate ionic impurities within the insulating supports.

The ESD Association Standard Test Method STM3.1 recognizes that a small
amount of self decay may be unavoidable. This test method allows a maximum
self-decay rate of 10% in five minutes. Self decay shortens decay time
measurements. A small amount of self decay doesn’t impact a CPM decay
measurement enough to matter. Higher self-decay rates present an error in
decay time measurements that may be significant to your evaluations of ionizers.

Minimizing Plate Self Decay

Relative humidity becomes a problem when it rises above 60%. Keeping your
CPM clean and storing it in a warm, dry area are the most effective ways to
manage plate self decay. The warm air lowers the relative humidity.

When the CPM is stored in areas with higher humidity, use a heat gun to warm
the insulative supports and drive out any moisture that has been absorbed by
those supports. This will offer a temporary solution if the relative humidity and
plate self-decay rate are too high.

When this method seems to ineffective, clean the supports with a solution of de­ionized water and isopropyl alcohol and allow the plate to dry for 24 hours.

Another Solution

Monroe Electronics’ newer CPM, Model 288, uses a high-voltage follower
(electrometer) technology that is much more resistant to the effects of high
humidity. We recommend this model for high-humidity areas where CPM
measurements are made.