MTI Instruments Technical Manual 7001-0029
Revision 4.0 – January 21, 2013
AccuMeasure™ 9000
Capacitance Sensor Amplifier
Users Manual
MTI Instruments Incorporated
325 Washington Avenue Extension, Albany, New York 12205 USA
█ Phone (518) 218-2550 or 800-342-2203 (USA Only) █ Fax (518) 218-2506
█ Web www.mtiinstruments.com █ Email sales@mtiinstruments.com
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Revision History
Rev 4.0 Release
ii
WARRANTY
Seller warrants to the Purchaser that equipment to be delivered hereunder which is of Seller's own
manufacture will be free from defects in material or workmanship and will be of the kind and quality
designed or specified in the contract. Any parts of the equipment which have been purchased by Seller
are warranted only to the extent of the original manufacturer's warranty.
This warranty shall apply only to defects appearing within 1 year from the date of shipment by Seller. If the
equipment delivered hereunder does not meet the above warranty, and if the Purchaser promptly notifies
Seller, Seller shall thereupon correct any defect, including nonconformance with the specifications, either,
at its option, by repairing any defective or damaged parts of the equipment, or by making available at
Seller's plant necessary repaired or replacement parts. No allowance will be made for repairs or
alterations made by others without Seller's written consent or approval. Seller assumes no responsibility
for damage caused by improper installation or by operation in violation of its rated operating condition,
intentional or otherwise, or by improper handling or maintenance. The liability of Seller under this warranty
(except as to title), or for any loss or damage to the equipment, whether the claim is based on contract or
negligence, shall not in any case exceed the cost of correcting defects in the equipment as herein
provided and upon the expiration of the warranty period of all such a liability shall terminate. The foregoing
shall constitute the exclusive remedy of the purchaser and the exclusive liability of the Seller.
The foregoing warranty is exclusive and in lieu of all warranties, whether written, oral, implied or statutory
(except as to title). There are no warranties which extend beyond those expressly stated in this contract.
FCC NOTICES
This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in
accordance with the manufacturer’s instruction manual, may cause interference with radio and television
reception. This equipment has been designed as a Class A digital device of the FCC rules. These limits
are designed to provide reasonable protection against harmful interference in a commercial installation.
However, there is no guarantee that interference will not occur in a particular installation. If this equipment
does cause harmful interference, which can be determined by turning the equipment off and on, you are
encouraged to try to correct the interference by one or more of the following measures:
Relocate the instrument with respect to the other device.
Plug the instrument into a different outlet so that the instrument and the other device are on
different branch circuits.
If necessary, consult a representative of MTI Instruments. You may find the following booklet helpful: FCC
Interference Handbook, 1986, available from the U.S. Government Printing Office, Washington, D.C.
20402, Stock No. 004-000-00450-7.
Information in this manual is subject to change without notice.
© 2013 MTI Instruments
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SAFETY WARNINGS
Warning Symbol Definitions
DISCLAIMERS
Language Requirements
Use Requirements
Use Requirements
Electrical Shock Hazard Areas
Electrical Shock/Electrocution Hazard.
DISCLAIMER: EU LANGUAGE REQUIREMENTS
This is the Original Instructions version of the User Manual. It is illegal to
operate this equipment in a European Union (EU) Member State unless the
manual is written in an official language of the Member State. Contact MTI
Instruments for the availability of translated manuals.
WARNING: ELECTRICAL SHOCK/ELECTROCUTION HAZARD
This equipment is connected to AC mains power. There are no user
serviceable parts within the controller box. Do not attempt to open the
controller box or insert foreign objects into the box vent openings.
DISCLAIMER: USE OTHER THAN INTENDED PURPOSE
Using this product in a manner or a purpose other than the manner or purpose
specified by the manufacturer may impair the safety features of this product.
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TABLE OF CONTENTS
SAFETY WARNINGS III
DISCLAIMERS III
TABLE OF CONTENTS ............................................................................................................................... IV
1 INTRODUCTION 1
1.1 ACCUMEASURE™ 9000 SYSTEM DESCRIPTION ....................................................................................1
1.2 PROBE AMPLIFIER SPECIFICATIONS......................................................................................................2
1.3 PROBE SPECIFICATIONS ......................................................................................................................3
1.4 RECEIVING INSPECTION PROCEDURE ...................................................................................................4
1.5 RETURN SHIPMENT PROCEDURE..........................................................................................................5
2 OPERATING PRINCIPLES 6
3 INSTALLATION INSTRUCTIONS 8
3.1 POWER REQUIREMENTS ......................................................................................................................8
3.2 CONNECTIONS ....................................................................................................................................9
3.3 CONTROL SWITCHES.........................................................................................................................13
3.4 DISPLAYS..........................................................................................................................................13
3.5 PROBE MOUNTING............................................................................................................................. 14
3.6 PROBE CABLES .................................................................................................................................15
3.7 TARGET GROUNDING.........................................................................................................................15
3.8 STATIC ELECTRIC DISCHARGE PRECAUTION.......................................................................................15
4 OPERATING INSTRUCTIONS 16
4.1 PROBE AMPLIFIER CALIBRATION CHECK............................................................................................. 16
4.2 PUSHED AMPLIFIERS AND PROBES .....................................................................................................18
4.3 CONDUCTIVE TARGET THICKNESS MEASUREMENTS............................................................................19
5 TROUBLESHOOTING 20
1
1 INTRODUCTION
1.1 Accumeasure™ 9000 System Description
The Accumeasure System 9000 amplifier is a high-precision single or dual-channel capacitance probe
amplifier that uses standard or custom MTI noncontact probes. Its analog output voltage is proportional to
the gap between a probe and its measurement target. A front-panel bargraph is available for each probe
channel to indicate the probe gap value. This indicator is used for initial probe gap setup and for periodic
monitoring of the magnitude of the average gap. An optional digital panel meter is available in place of the
bargraph to provide a numerical indication of the probe gap. This meter is calibrated to indicate a voltage
reading proportional to the rear panel output signal voltage.
The probes measure displacement from the probe face to the target and are connected to the amplifier
with special low-noise coaxial cable. The cable’s outer shield is electrically driven to cancel the cable’s
parasitic capacitance and ensure the highest linearity. Front-panel gain and offset controls permit minor
adjustments of the probe calibration characteristics.
An internal 5-pole Butterworth low-pass filter removes unwanted high-frequency noise for the best
resolution possible. Optional filter cutoff frequencies of 10 Hz, 500 Hz, 1 kHz, 2 kHz and 5 kHz are
available.
Two separate factory preset calibrations are offered. The primary calibration produces an analog output
proportional to the probe range divided by 10 volts. For a probe with a 1mm (0.039inch) range and a 10V
full-scale output, the analog output is 0.1mm per volt (0.0039inches per volt).
The second type of calibration produces a normalized 0.025m per millivolt (0.98 micro-inch per millivolt)
calibration slope when used with any MTI probe. With this type of calibration, a 1mm (0.039 inch) range
probe would have a range of 200m (7.8mils), a 0.025m per millivolt (0.98 micro-inch per millivolt)
sensitivity factor, and a standoff of 1mm (0.039 inches). The advantage of this type of calibration is that
any probe type will have the same sensitivity factor of 1 micro-inch per millivolt, regardless of its range.
2
1.2 Probe Amplifier Specifications
Output Signal: 0-10VDC Nominal
Maximum Adjustable Offset: -5V (provides and output of -5 to +5VDC)
Measurement Range2: 0-12.5mm (0.500inch)
Dynamic Resolution3: 0.000075%/√Hz FSR RMS
Linearity4: ±0.02% FSR
Repeatability
±0.01% FSR
Frequency Response (Factory Selectable): DC-5kHz
Warm-up Up time 1 Hour
Temperature Stability: ±0.01% FSR/ºC
Time Stability
±0.01% FSR/100 hours
Output Signal7: 0-10VDC
Power: 100 to 240VAC, 50/60Hz, 20 Watts
Operating Temperature: 4 to 40ºC (40 to 100ºF)
Storage Temperature: -15 to 65ºC (5 to 150ºF)
Dimensions (LxWxH): 241x165x56mm (9.5x6.5x2.2”)
Mass : 2.3kg (5lbs)
Probe Voltage : 8.5Vrms Max
Bargraph : Proportional to gap, 10% of range per bar.
All specs require that the probe is factory matched to the amplifier. Cable length is 2.5m. Freq is 500Hz.
Dependant on probe type selected.
100-5kHz. Equivalent to 0.00167% FSR @500Hz RMS.
After 100hours site acclimation, warm up, 20ºC,100kPa,50% (Temperature, Pressure, Humidity).
After 100hours site acclimation, warm up, 20ºC,100kPa,50% (Temperature, Pressure, Humidity).
After 100hours site acclimation, warm up, 20ºC/100kPa/50% (Temperature, Pressure, Humidity).
Signal Proportional to probe gap.
1
5
6
1
2
3
4
5
6
7
3
1.3 Probe Specifications
Temperature Rating: Standard Probes: -130 to 205ºC (-200 to 400ºF)
Probe Connector (if equipped): -65 to 105ºC (-85 to 220ºF)
Cable: -90 to 200ºC (-130 to 390ºF)
Cable Termination at Amplifier: -65 to 165ºC (-85 to 330ºF)
High-temperature, Cryogenic, and Vacuum compatible probes
are available. Contact the factory.
Accuracy: ±0.05% of range when calibrated to a known standard.
Probe Cable Interchangeability: Accurate within ±0.5% of range without recalibration
Pressure Rating: Standard, 1400kPa (200psig). Higher pressure probes available.
Contact factory.
Cable Length: 2.5m (8.2ft)
Construction: 304 stainless steel standard. Lower coefficient of thermal
expansion designs available. Contact factory
4
1.4 Receiving Inspection Procedure
The Accumeasure™ 9000 is shipped from MTI fully assembled and packed in a cardboard carton with
foam inserts to guard against shipping damage. Upon receipt, perform the following procedure before
using the unit to perform dimensional measurements:
1. Inspect the exterior of the shipping carton. Note any obvious damage. If shipping damage is
evident, file a claim with the carrier.
2. Remove the instrument from the shipping carton. Inspect the instrument's exterior for any signs of
damage.
3. Apply AC power to the unit and place the power switch the “ON” position.
4. The front panel POWER indicator, and the bargraph(s) or optional digital panel meter(s) should be
illuminated. Without a probe cable(s) attached to the probe connector on the front panel, all of the
bargraph display segments should be fully illuminated. Instruments with the optional digital panel
meter should indicate a voltage higher than +10.0 VDC.
5. Place the front panel OFFSET switch(s) in the “out” position.
6. Attach a coaxial cable from the channel 1 output signal connector on the rear panel to a digital
voltmeter. The voltmeter reading should be higher than +10.000 VDC.
7. If the unit is an Accumeasure 9000-2, attach a coaxial cable from the channel 2 output signal
connector on the rear panel to a digital voltmeter. The voltmeter reading should be higher than
+10.000 VDC.
8. If any problems were found with the front-panel display(s) or with the output signal amplitude(s),
contact MTI at 1-518-218-2550.
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1.5 Return Shipment Procedure
Contact MTI at 1-518-218-2550 to receive return authorization prior to shipping the instrument. Reference
the instrument's name, model and serial numbers on all correspondence. Be sure to include a brief
description of the reason for the return. Place the instrument in the original shipping carton (if available)
and forward prepaid to:
MTI Instruments, Inc.
Supervisor of Manufacturing
325 Washington Avenue Extension
Albany, NY 12205-5505
Mark "RMA" and the RMA number (if a number is issued) on the outside of the box. If the original packing
materials are not available:
1. Wrap the instrument in plastic or heavy paper.
2. Place packing material around all sides of the instrument and pack it in a cardboard carton.
3. Place instrument and inner container in a sturdy cardboard carton or wooden box.
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2 OPERATING PRINCIPLES
AccumeasureTM System measurement technology is based on the principle of parallel plate capacitor
measurement. The electrical capacitance formed between an AccumeasureTM probe and a target surface
varies as a function of the distance (gap) between these two surfaces. This function can be stated as:
Figure 1: Capacitance Probe Physics
7
The AccumeasureTM System measures the electrical impedance of the capacitance between a sensing
electrode in the probe and a ground-referenced target. The magnitude of the impedance is proportional to
the reciprocal of the capacitance value as defined by the equation below:
C
Z
c
1
where:
is proportional to the frequency at which the capacitance measurement is performed.
Substituting the equation for capacitance into the impedance equation shows that the impedance is directly
proportional to the gap value D, as shown in the following equation:
A
D
Z
C
The AccumeasureTM probe amplifier produces a DC voltage that is linearly proportional to the average value
of the probe gap impedance, and an AC voltage variation from the DC voltage that is directly proportional to
the amplitude of the target vibration. The amplifier electronic circuitry eliminates the effects of both the probe
cable capacitance and the stray capacitance at the edge of the probe sensing area that could cause nonlinearity of the gap and vibration measurements.
The standard probe cable length is 2.5m (8.2ft) and standard full scale gap probes from 25um to 5mm
(0.001 to 0.200 inches) are available. Custom cable lengths from 300mm to 15m (1 to 50ft) and custom
probes from 12.5um to 12.7mm (0.0005 to 0.5 inches) can be used with the AccumeasureTM probe
amplifier. Contact the factory for details on custom cables and/or probe lengths.
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3 INSTALLATION INSTRUCTIONS
3.1 Power Requirements
The Accumeasure System 9000 unit may be powered by either a 50-Hz or 60-Hz power source with a
voltage ranging from 100 to 240 Vac. No changes in the unit setup are required for power source voltages
in this range. The unit has a standard IEC 320, 3-conductor power receptacle on rear panel for attachment
of the power cable and a power switch on the power input assembly. Refer to the Connections section
(pg. 10) and the Control Switches section (pg. 14) for the exact locations of components.
To change the power line fuse, use the following procedure:
1. Remove the power cord from the rear panel power receptacle.
2. Pry up one end of the power receptacle cover by inserting the blade of a small screwdriver under
the tab next to the CORCOM lettering.
3. Rotate the receptacle cover to provide access to the red fuse holder.
4. Remove the red fuse holder from the receptacle by pulling it straight out.
5. Remove the suspected open fuse and replace it with a .4 amp, 5mm X 20mm slow blow fuse,
type Bussman S506. The amperage rating is also listed on the rear panel of the Accumeasure
System 9000 unit.
6. Insert the red fuse holder into the receptacle with the fuse toward the bottom of the unit.
7. Rotate the receptacle cover back in place until it snaps securely into the receptacle.
8. Insert the power cord into the receptacle and apply AC power to the unit.
9
3.2 Connections
The Accumeasure 9000 probe amplifier unit requires four connections for operation:
The probe cable(s)
The target ground
The output signal(s)
The AC power cable.
The probe cable(s) should be connected to the BNC connector(s) labeled INPUT on the front panel of the
Accumeasure 9000-1 (see Figure 3: Accumeasure™ 9000-1 Front Panel – Digital Display or Figure 2:
Accumeasure™ 9000-1 Front Panel – Bargraph Display) or the Accumeasure 9000-2 (see Figure 5:
Accumeasure™ 9000-2 Front Panel-Digital Display or Figure 4: Accumeasure™ 9000-2 Front PanelBargraph Display).
Connect the Accumeasure 9000 to a standard AC power source with the provided three-wire IEC 320,
power cable plugged into the rear panel (see Figure 7: Accumeasure™ 9000-1 Rear Panel or Figure 6:
Accumeasure™ 9000-2 Rear Panel).
The target ground wire should be connected to the black, binding post labeled GROUND on the rear
panel (see Figure 7: Accumeasure™ 9000-1 Rear Panel or).
The displacement voltage output signal(s) is available from the BNC connector(s) labeled 1, 2, and SUM
on the rear panel (see Figure 7: Accumeasure™ 9000-1 Rear Panel or).
The output impedance of all outputs is 50 ohms. Any good quality coaxial cable or twisted pair cable,
shielded or unshielded, up to a length of 100 feet (30 meters) can be used to connect to other equipment
(refer to pg.14 for the recommended load impedance on the Signal Output connectors).
NOTE
The shield/braid of the probe cable and connectors is driven at the probe carrier voltage and cannot be grounded.
Most commercially available pass-through fittings tie the outer conductor to the chassis, thus grounding the shield.
When using extension cables, insulate the connections so that they do not come in electrical contact with the
equipment chassis
The shield integrity of the probe cable cannot be broken. If the probe cable is damaged, it is recommended that it be
replaced rather than repaired.
10
!
Power Indicator
Bargraph Display
Gain Adjustment
Offset Switch & Indicator
Offset Adjustment
Probe Input
Offset Switch & Indicator
Offset Adjustment
Digital Display
Power Indicator
Gain Adjustment
!
Figure 3: Accumeasure™ 9000-1 Front Panel – Digital Display
Figure 2: Accumeasure™ 9000-1 Front Panel – Bargraph Display
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Channel 2 Bargraph Display
Probe Input
Channel 2
Probe Input
Channel 1
Channel 1 Offset Switch & Indicator
Channel 1 Offset Adjustment
Channel 1 Gain Adjustment
Channel 2 Offset Switch & Indicator
Channel 2 Offset Adjustment
Power Indicator
Channel 2 Gain Adjustment
!
Channel 1 Bargraph Display
!
Channel 1 Offset Switch & Indicator
Channel 2 Offset Switch & Indicator
Probe Input
Channel 1
Probe Input
Channel 2
Channel 2 Offset Adjustment
Channel 2 Digital Display
Channel 1 Digital Display
Channel 2 Gain Adjustment
Channel 1 Gain Adjustment
Power Indicator
Channel 1 Offset Adjustment
Figure 4: Accumeasure™ 9000-2 Front Panel-Bargraph Display
Figure 5: Accumeasure™ 9000-2 Front Panel-Digital Display
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Signal Output
Ground Connection
Power Cable Connection
Fuse
On/Off Switch
Signal Output
20 W
50/60 Hz
1
100-240 VAC
T 0.4A, 250V
Signal Output
Signal Output
Ground Connection
Power Cable Connection
Fuse
On/Off Switch
Signal Output
21
20 W
T 0.4A, 250V
100-240 VAC
50/60 Hz
SUM
Figure 6: Accumeasure™ 9000-2 Rear Panel
Figure 7: Accumeasure™ 9000-1 Rear Panel
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Do not attempt to make adjustments other than calibrating the probe amplifier gain and offset controls on
the front panel. The unit is calibrated at the factory to perform within published specifications. If this
performance is not attained in the field, check for damaged cables, poor grounding, or a damaged probe.
3.3 Control Switches
The Accumeasure™ 9000 control switches that are used during the installation are:
The AC power ON/OFF switch.
The external offset switch for each probe amplifier channel.
The AC power ON/OFF switch is located on the rear panel mounted power input module next to the
power cable attachment receptacle. Figure 7: Accumeasure™ 9000-1 Rear Panel and Figure 6:
Accumeasure™ 9000-2 Rear Panel indicate the switch location. The position of this “rocker-type” switch
controls the application of AC power line voltage to the Accumeasure 9000 unit. Pressing the “I” side of
the switch connects the AC voltage to the unit and turns the unit “ON”. Pressing the “O” side of the switch
disconnects the AC voltage, on turns the unit “OFF”.
Each probe amplifier channel has an external offset switch that is located on the Accumeasure 9000
front panel. The exact switch locations are shown on Figure 3: Accumeasure™ 9000-1 Front Panel –
Digital Display, Figure 2: Accumeasure™ 9000-1 Front Panel – Bargraph Display, Figure 5:
Accumeasure™ 9000-2 Front Panel-Digital Display, and Figure 4: Accumeasure™ 9000-2 Front PanelBargraph Display. These switches are “push-on/push-off”, alternating position type switches that move in
and out 2.5mm (0.1”) with each alternate push operation. The function of the switch is to engage and disengage the front panel accessible offset control that is used to perform in-place probe calibration (see 4.1
Probe Amplifier Calibration Check). The external offset potentiometer is dis-engaged when the
switch is set to its “out” position. The control is engaged for offset adjustment when the switch set to its
“in” position. The offset switch indicator above the switch lights when the switch is “in” to indicate that the
external offset potentiometer is engaged. During the initial installation testing of the Accumeasure 9000
the external offset switch(s) should be positioned in the “out” position, with the offset switch indicator not
lighted, so that the factory offset calibration is being tested.
3.4 Displays
Displays included on the Accumeasure 9000 unit are:
The Power Indicator
The Offset Switch Indicator
The Bargraph Display
The Optional Digital Panel Meter
The power indicator is a green LED lamp that is lighted whenever AC power line voltage is connected to
the unit by the power ON/OFF switch. The power indicator is located on Accumeasure 9000 front panel
at the position shown on Figure 3: Accumeasure™ 9000-1 Front Panel – Digital Display, Figure 2:
Accumeasure™ 9000-1 Front Panel – Bargraph Display, Figure 5: Accumeasure™ 9000-2 Front PanelDigital Display, and Figure 4: Accumeasure™ 9000-2 Front Panel-Bargraph Display.
Each probe amplifier in the Accumeasure 9000 has a front panel located offset switch indicator to
indicate when the external offset potentiometer is engaged. The location of this indicator, above the
external offset switch for each channel, is shown on Accumeasure 9000 front panel at the position shown
on Figure 3: Accumeasure™ 9000-1 Front Panel – Digital Display, Figure 2: Accumeasure™ 9000-1 Front
NOTE
The output impedance of the rear panel signal output BNC connector(s) is 50. When connecting to
an instrument such as a volt meter or an analog to digital converter, the input impedance of the
instrument must be greater than 100k. Failure to due so will result in an apparent calibration error.
14
Panel – Bargraph Display, Figure 5: Accumeasure™ 9000-2 Front Panel-Digital Display, and Figure 4:
Accumeasure™ 9000-2 Front Panel-Bargraph Display. The offset switch indicator is a blue, LED lamp
that is lighted when the offset switch is positioned in its “in” position and the front panel located, external
offset potentiometer, is engaged.
The Accumeasure 9000 probe amplifier has a bargraph display on the front panel to indicate the value of
the probe-to-target gap. Each bargraph is a ten element, green LED array that is calibrated to display,
within +/-5% of the full scale probe range, the relative gap value. The number of display elements lighted
indicates the gap magnitude. For instance, for a gap value between touch and 10% of the full-scale gap,
only the left element is lighted, and for a gap value between 50% and 60% of full scale, the six left
elements are lighted. The location of the bargraph display(s) is shown on Figure 2: Accumeasure™
9000-1 Front Panel – Bargraph Display and Figure 4: Accumeasure™ 9000-2 Front Panel-Bargraph
Display.
A back lighted, digital panel meter to display the probe gap signal for each probe channel is available, as
an option, to replace the bargraph display in the Accumeasure 9000. The meter has a 3 1/2 digit display
that is calibrated to produce a reading equal to the rear panel output signal voltage with a full scale range
of +/-10.00 VDC. The meter has a resolution of 0.01 VDC, and an accuracy of +/-0.02 VDC. The location
of the digital display(s) is shown on Figure 3: Accumeasure™ 9000-1 Front Panel – Digital DisplayFigure
5: Accumeasure™ 9000-2 Front Panel-Digital Display.
3.5 Probe Mounting
Since AccumeasureTM9000 measures probe-to-target gap, the probe fixture must have good mechanical
stability and alignment. The fixture must hold the probe securely and maintain the probe face parallel to
the target surface. Probe tilt causes measurement errors, so a tilt of less than 5% of range is
recommended. That would mean that for a 500um (20 mil) range sensor, the edge of the sensor should
tilt no more than 25um (1 mil) on a side.
It is recommended that the probe fixture be connected to the same ground return as the target if the target
is grounded. The fixture should have a noise-free, low-impedance return path to the DC supply ground of
the power supply that provides the DC voltages to the AccumeasureTM9000 single channel probe
amplifier board unit. Values of up to 1 kilo-ohm resistance may be tolerated under certain conditions, such
as when maximum system linearity and resolution are not required.
If a direct ground connection is not possible, a capacitive-coupled connection can be used. Be aware that
a 350pF value in the return path will introduce a small amount of measurement noise. Larger
capacitances will introduce correspondingly smaller amounts of noise (1000pF or larger is recommended).
In practice, the ground return path may be provided automatically if the target is at ground potential and is
connected back to the amplifier ground connector through the ground terminal on the AC supply line. To
minimize the measurement noise, connect a ground lead directly from the probe fixture and target to the
ground connector on the probe amplifier module.
The probe should be mounted to meet two important conditions:
1) At a minimum excursion, the probe-to-target gap should be no less than 5% of the probe range.
2) At maximum excursion, the target gap must not exceed 95% of the full-scale probe range.
Before performing a measurement, ensure that the probe and target under test are clean and free from
debris.
CAUTION
The probe connector and the probe body on ASP-1, ASP-2, ASP-5, and ASP-10 probes carry a 3 to
5Vrms electrical guard voltage for the cable shield and the probe. These must not be shorted to ground
by the fixture or the system will be inoperative.
15
3.6 Probe Cables
MTII capacitance probes are equipped with special, low-noise coaxial cables. Standard coaxial cables are
not acceptable for connecting the probes to probe amplifier. Cables are available in either 50-ohm or 95ohm sizes. Specifications:
Diameter
Operating Temperature
50Cable
1.95mm (0.076 inch)
-90 to +200ºC (-130 to 390ºF)
95Cable
1.6mm (0.063 inch)
-90 to +200ºC (-130 to 390ºF)
Table 1: Standard Probe Cable Characteristics
Most probes are shipped with 95, low noise cables. If cable size is important, please contact the factory.
Cables may be spliced only if the spiced section is 100% shielded. Routing the cable through relays and
other switching devices will interfere with the measurement system.
Cylindrical feed-through assemblies may be used. Since the cable shield is not at ground potential, the
feed-through must have provisions that guarantee that the cable shield will be isolated. This is typically
accomplished by selecting a triaxial feed-through, utilizing the center and middle conductors and allowing
the outside conductor to ground with the equipment. When selecting a triaxial feed-through, it is also
important that the center conductor (tip) of remain 100% shielded by the middle (fringe guard conductor).
Contact the factory for information on MTII-manufactured feed-through assemblies.
3.7 Target Grounding
The target being measured by the probes connected to the Accumeasure™ 9000 must be grounded
directly to the board power supply grounds for the probe to target gap to be accurately measured.
In general, it is recommended that grounding practices for sensitive equipment be applied when using the
AccumeasureTM amplifier. For additional information on grounding practices refer to H.W. Ott’s Noise
Reduction Techniques in Electronic Systems (John Wiley and Sons, 1976) or to Chapter 24 of the Analog
Devices Applications Reference Manual (1993).
3.8 Static Electric Discharge Precaution
The face of the probe and the center conductor of the BNC for probe input is static
sensitive. Due to the nature of capacitance amplifiers it is possible to damage the
sensitive input circuitry if there is a static electric discharge into the center conductor of
the probe input BNC or the center sensing area of the probe itself. Protection circuitry
has been incorporated to minimize this effect but a discharge of sufficient amplitude
will cause damage. The probes may be handled without ground straps, but high static
charges on the target may arc over to the probe.
!
NOTE
A poor ground return and the connection of the board output connectors to equipment such as
oscilloscopes, chart recorders, or data loggers can create ground loops, which will cause errors due to
excessive of 50-60 Hz noise on the carrier and gap output signals.
16
4 OPERATING INSTRUCTIONS
4.1 Probe Amplifier Calibration Check
It may be necessary to check and adjust the amplifier calibration for applications which require maximum
accuracy or when the probe and amplifier have been ordered separately. The best results are obtained
when a calibrated micrometer is used as the probe-positioning device. If this is not available, a standalone micrometer such as the MTI KD-CH-IIID calibration stand may be used.
The gain and offset controls on the Accumeasure front panel can be used to calibrate the probe. A slight
tilt of the probe in a fixture also may introduce a gain or offset error that may be eliminated through
calibration.
RECOMMENDED EQUIPMENT
1. A Voltmeter with a minimum resolution of 0.0001VDC and accuracy of ±0.001VDC.
2. A Micrometer with a minimum resolution of 0.05% of the probe range (if available) and accuracy
of ±0.1% of the probe range. (An MTI KD-CH-IIIA Calibration Fixture may be used for this
purpose; refer to the KD-CH-IIIA Operating Instruction Manual to compare the fixture resolution to
the calibration requirements.)
BASIC CALIBRATION
Perform calibration by adjusting the front-panel GAIN and OFFSET controls. Offset is adjusted while the
probe is at 10% of range. Gain is adjusted at 100% of range. Use the following procedure:
1. Set the voltmeter to monitor the output of the amplifier.
2. With the unit turned off, adjust the probe so it is lightly touching the target.
3. Zero the micrometer and then move it back to 10% of the intended range. Turn the unit back on.
4. Press in the OFFSET switch on the front panel of the AS-9000 and adjust the front-panel control
for OFFSET until the output reads 1.000 VDC.
5. Move the micrometer to 100% of range and adjust the GAIN control until the output reads 10.000
VDC.
6. Readjust the micrometer to 10% of range and recheck the 10% point
(1.000 V). Readjust OFFSET if necessary, and recheck the 100% limit.
7. Repeat steps 5 and 6 until the voltage at 10% of range is 1.000 ±0.001 VDC and the voltage at
100% of range is 10.000 ±0.001 VDC.
8. Verify several points between the minimum and maximum limits.
If this procedure does not produce the desired system accuracy, more elaborate calibrations such as
linearizing the output may be accomplished by readjusting internal potentiometers. These adjustments
must be made at the factory or by a qualified MTI representative.
WARNING
Under no circumstances should you adjust pots on the internal boards. These pots control the CMRR (common
mode rejection ratio), balance, and other amplifier parameters and should only be adjusted at the factory.
Opening the product voids any warranty or factory calibration certification.
17
NORMALIZED CALIBRATION
When the Accumeasure System 9000 has been calibrated by the factory with a 1mv/1uinch, Normalized
calibration, follow the procedure below to check the calibration. The gap at which the output voltage is
zero has been set at the factory to a customer specified value, and the output voltage will increase in
positive direction with a 1mv/uinch slope for increasing an gap value from the specified zero gap.
Perform this calibration by adjusting the front-panel GAIN and OFFSET controls. Offset is adjusted while
the probe is at the specified zero output voltage, gap value. Gain is adjusted to produce the 1mv/1uinch
slope over the gap range between the specified zero voltage gap value and the full scale gap for the probe
that has been factory calibrated with the system. Use the following procedure:
1. Set the voltmeter to monitor the output of the amplifier.
2. With the unit turned off, adjust the probe so it is lightly touching the target.
3. Zero the micrometer and then rotate it to produce the specified zero output voltage gap value.
Turn the unit back on.
4. Press in the OFFSET switch on the front panel of the AS-9000 and adjust the front-panel control
for OFFSET until the output reads 0.000 VDC.
5. Rotate the micrometer to produce an air gap equal to the maximum probe range value for the
probe provided with the system. The full range value is a function of the probe used and the zero
voltage gap value. For example, a 20 mil range probe, with a 5mil zero voltage gap value will have
a full range gap value of 15 mils because the output voltage is 10 volts at this gap with the
1mv/1uinch slope.
6. Adjust the GAIN control to produce an output voltage equal to 1mv/1uinch slope multiplied by the
full range gap value minus the zero voltage gap value. For example, a 20 mil range probe with a
zero voltage gap of 5 mils will have an output voltage of:
(1mv/(1uinch) x (15mils-5mils) x (1000uinch/1mil) = 10000mv.
The output voltage will be: (10000mv) x (1v/1000mv) = 10.000VDC
7. Readjust the micrometer to produce the zero output voltage gap and check for a 0.000 VDC
output voltage. Readjust OFFSET to produce the zero output voltage if necessary.
8. Recheck the voltage at the full range gap and readjust the output voltage if necessary.
9. Repeat steps 7 and 8 until the output voltage is zero at the zero voltage gap, and the full range
gap voltage is correct.
10. Verify several points in the linear probe range to ensure that the slope is 1mv/1unich.
If this procedure does not produce the desired system accuracy, more elaborate calibrations such as
linearizing the output may be accomplished by readjusting internal potentiometers. These adjustments
must be made at the factory or by a qualified MTI representative.
18
4.2 Pushed Amplifiers and Probes
Some applications require probes that have small diameters yet achieve the sensing ranges of largerdiameter probes. For example, a 500um (20mil) range would normally require an ASP-20-CTA probe with
a diameter of 11.1mm (0.437 inch) used with a standard amplifier. If a smaller probe diameter is required,
the amplifier may be “pushed” by a factor of 2. This would allow smaller sized probes, such as an ASP-10CTA, with a diameter of 6.25mm (0.250 inch) to be operated over a 500um (20mil) range.
Similar effects can be achieved with other combinations of probe range and amplifier push. There are
limitations to the amount of push that can be achieved and this is dependant on several factors, including
probe type and cable length. The maximum push recommended is 40X.
When employing “pushed” amplifier and probe combinations, the output versus distance must be
individually calibrated in order to obtain maximum accuracy and linearity. The level of output noise
generated by the “pushed” amplifier also increases in amount equal to the push factor.
For example, a standard probe amplifier with an ASP-10 probe and a 2.5m (8.2ft) cable has an output
noise level of 1.0±0.2mVpp at a 250um (10mil) probe-to-target air gap. A 5X pushed amplifier working with
the same probe and cable will have a 5.0 ±1.0mVpp output noise at the same gap.
It is recommended that you contact an MTII representative or factory applications personnel for more
information on pushed probe and amplifier combinations.
19
4.3 Conductive Target Thickness Measurements
The dual probe amplifier, Accumeasure System 9000-2 may be used to perform thickness
measurements. The probe amplifier summation circuit in the 9000-2 unit should be set to produce a
[Channel 1 + Channel 2] summation for the correct addition of the two probe signals (contact MTI if there
is a question about the exact configuration of the summation circuit). With the 9000-2 unit set up to
perform the thickness measurement, the rear panel located, Sum Signal Output (refer to Figures 3-5 and
3-6, on pg.13) produces an output that has an increasingly positive magnitude as the target thickness
decreases.
MEASUREMENT PROCEDURE
1. Fixture the probes on opposite sides of the target with the centerline of the two probe sensing
faces directly in line with each other. Remove the target and set the air gap between the probe
sensing faces so it is equal to the mean thickness of the target plus the sensing range of probes.
6mm (0.236 inches) and probes with a range of 1.5mm (0.059 inch) are being used, the total gap
between the probe faces would be set at approximately 9mm (0.354 inch). Make sure the probeto-target air gap for Probe 1 and Probe 2 does not exceed the measuring range of the probes.
2. Connect the probes to the Accumeasure System 9000.
3. Place a target with known thickness midway between the probes. This test target should be the
same thickness as the object that will be gauged.
4. Ground the target.
5. Connect a digital voltmeter (DVM) or oscilloscope (whichever is used) to the Channel 1 output.
6. Adjust the probe gap until the output voltage is between 0 and +10V (+5 to +7 volts is ideal). Keep
in mind the maximum excursion of targets to be gaged. The output voltage (gap) should not
exceed the linear range of the probe.
7. Press the Channel 1 offset switch on the front panel until the blue “offset on” LED is lit. Adjust the
offset control to 0 volts.
8. Connect the DVM or oscilloscope to the Channel 2 output and repeat steps 6 and 7 for Channel 2
output.
9. Connect the DVM or oscilloscope to the sum signal output on the rear panel. It should read 0
volts, corresponding to the test target thickness. Thicker targets will read as positive numbers on
the meter display. Thinner targets will read as negative displacement values.
10. To determine thickness, multiply the voltage change by the probe sensitivity factor. For example,
1.27mm (50 mil) range probes have a sensitivity factor of 0.127um (5 mils) per mV. If the output
signal increases by +20mV, then the target is increasing in thickness by 2.54um (100 mils).
THICKNESS MEASUREMENTS NOTES
1) A very large guard signal in close proximity to an adjacent very low signal can easily cause a 1%
thickness error. Therefore, when possible the probe cables should not be routed in close
proximity to each other.
2) The fixtures that hold the probes can contribute significantly to poor readings. Use of low
coefficient of thermal expansion materials, isothermal designs, and capturing the probes as close
to their measurement ends as possible can help minimize drift effects.
3) The field from the probes can interact with adjacent and proximate conductors. For example, a
probe that is operating in a well can couple to the walls of the well and produces erroneous
effects. It is recommended that the well diameter be 50% greater than the probe outer diameter
to ensure linear operation at large gaps. It may be necessary to re-calibrate the probes if they are
operating in recessed conditions.
4) Avoid target tilt errors. Range-extended probes (“pushed probes”) are less susceptible to target tilt
error. However, noise increases with push. Target tilt warps the capacitance field, starting at the
point of the target’s closest approach. Using smaller probe sensing areas with large air gaps will
minimize the tilt effect.
5) For thickness measurement of non-conductive, dielectric materials contact MTII to obtain
application notes that describe the use of the AccumeasureTM System on non-conductive targets.
20
5 TROUBLESHOOTING
Accumeasure™ 9000 Probe Amplifier modules require specialized servicing techniques and should not be
serviced in the field. The troubleshooting table in this section should help you determine if the problem
exists in the Accumeasure equipment or in your auxiliary equipment. If the trouble is in the Accumeasure
System 9000, it should be returned to the factory for servicing.
Before following the troubleshooting procedure:
1. Set up a probe and grounded target so that probe-to-target gap is within the probe full scale
range,
2. Connect the probe to the Accumeasure™ 9000 Probe Amplifier with an MTI probe cable,
3. Apply AC power within the specified operating range to the Probe Amplifier.
4. Set the Probe Amplifier controls so the Accumeasure™ 9000 is within normal operating
conditions.
CAUTION
Observe all electrical safety precautions when performing maintenance.
21
PROBLEM
CORRECTIVE ACTION
REFERENCE
Front-panel power
indicator is not
lighted.
1. Check the AC power source for a
voltage between 100 and 240 VAC.
2. Check the rear panel power switch
position.
3. Check the AC power line fuse.
4. Contact MTI if the power and fuse are
not faulty and the power indicator will
not light.
1. INSTALLATION INSTRUCTIONS
manual section for component locations.
2. POWER REQUIREMENTS manual
section for fuse replacement.
Power indicator is
lighted but none of
the bargraph
display segments
for the probe
channel under test
is lighted, or the
optional digital
panel meter for the
channel under test
is indicating close
to zero volts DC.
1. Disconnect the coaxial probe cable from
the front panel receptacle. If bargraph
lights, or the optional digital panel meter
reads higher than +12 VDC, check the
cable for shield to center short circuit,
and probe for interelectrode short
circuits.
2. If jumper changes on the probe
amplifier board have been performed
since the unit has been received from
MTI, contact MTI to review jumper
selection.
1. INSTALLATION INSTRUCTIONS
manual section for component locations
Rear-panel output
voltage is zero for
the channel under
test, no voltage
change with probe
gap.
1. If jumper changes on the probe
amplifier board have been performed
since the unit has been received from
MTI, contact MTI to review jumper
selection.
2. If the bargraph indicator, or optional
digital panel meter is lighted, but does
not change with probe gap variation,
contact MTI. The problem may be a
faulty probe amplifier board or a cable
connection problem.
3. If the bargraph indicator, or optional
digital panel meter is lighted, and it
changes with the probe gap variation,
check the cables connected to the rear
panel signal output connector for a
short circuit condition.
1. INSTALLATION INSTRUCTIONS
manual section for component locations.
22
PROBLEM
CORRECTIVE ACTION
REFERENCE
The rear panel
output voltage is
not +10.00 VDC at
the full-scale probe
gap or +1.00 VDC
at 10% of full-scale
probe gap.
1. Check the front panel offset switch
position. If the offset indicator is lighted,
press and release the offset switch to
remove the offset.
2. Check that the range of the probe under
test is correct.
3. Verify that the probe and target are
touching when the probe gap should be
zero.
4. Check the calibration of the front panel
GAIN adjustment.
5. Ensure that the ground return
connection from the target to the unit is
intact.
1. PROBE AMPLIFIER CALIBRATION
CHECK for gain adjustment.
2. PROBE MOUNTING manual section.
The rear-panel
output voltage is
higher than
+12 VDC at all
probe-to-target gap
settings and all the
bargraph elements
for the channel
being tested are
lighted.
1. Check the probe cable connection to
the front panel; ensure that the cable is
securely attached to the receptacle.
2. Check for an open circuit in the center
wire of the probe cable.
3. Check for open circuit in the probe
between the connector and the sensing
element on the probe face.
4. Ensure that the ground return
connection from the target to the unit is
intact.
1. TARGET GROUNDING manual section.
2. PROBE MOUNTING manual section.
The noise on the
rear-panel output
voltage is
abnormally high.
1. Check the probe and probe cable for
loose or high resistance connections.
2. Check along the length of the probe
cable for cuts or defects.
1. TARGET GROUNDING manual section.
2. PROBE MOUNTING manual section
Excessive 60-Hz
noise on the rear
panel output signal.
1. Check for a good AC power line ground
between the power source and the case
of the unit.
2. Ensure that there is a good low
resistance ground return connection
between the target and the unit.
1. TARGET GROUNDING manual section.
2. PROBE MOUNTING manual section
23
PROBLEM
CORRECTIVE ACTION
REFERENCE
Excessive drift of
the rear panel
output voltage.
1. Check the probe support fixture to
ensure the probe, and the fixture are
not loose.
2. Check the shield on the sensor cable
and the connectors in the sensor
cable signal path for 100% shield
integrity and connector cleanliness.
1. PROBE AMPLIFIER CALIBRATION
CHECK for gain adjustment.
2. PROBE MOUNTING manual section.
OTHER PRODUCTS
FROM MTI INSTRUMENTS
1510A Battery Powered Signal Simulator/Generator
Proforma™ 300 Semiconductor Wafer Qualification
and General Thickness measurement (Capacitance)
MicroTrak™ Laser Triangulation Displacement Sensor
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