PCB Piezotronics 8120-410A User manual

Model 8120-410A
Strain Gage Sensor Signal Conditioner
Installation and Operating Manual
For assistance with the operation of this product,
contact PCB Piezotronics, Inc.
Toll-free: 800-828-8840
24-hour SensorLine: 716-684-0001
Fax: [phone]
E-mail: [email protected]
Web: www.pcb.com

Manual 21354 Rev E
ECN 50523
Repair and Maintenance
PCB guarantees Total Customer Satisfaction through its
“Lifetime Warranty Plus” on all Platinum Stock Products
sold by PCB and through its limited warranties on all other
PCB Stock, Standard and Special products. Due to the
sophisticated nature of our sensors and associated
instrumentation, field servicing and repair is not
recommended and, if attempted, will void the factory
warranty.
Beyond routine calibration and battery replacements
where applicable, our products require no user
maintenance. Clean electrical connectors, housings, and
mounting surfaces with solutions and techniques that will
not harm the material of construction. Observe caution
when using liquids near devices that are not hermetically
sealed. Such devices should only be wiped with a
dampened cloth—never saturated or submerged.
In the event that equipment becomes damaged or ceases
to operate, our Application Engineers are here to support
your troubleshooting efforts 24 hours a day, 7 days a
week. Call or email with model and serial number as well
as a brief description of the problem.
Calibration
Routine calibration of sensors and associated
instrumentation is necessary to maintain measurement
accuracy. We recommend calibrating on an annual basis,
after exposure to any extreme environmental influence,
or prior to any critical test.
PCB Piezotronics is an ISO-9001 certified company whose
calibration services are accredited by A2LA to ISO/IEC
17025, with full traceability to SI through N.I.S.T. In
addition to our standard calibration services, we also offer
specialized tests, including: sensitivity at elevated or
cryogenic temperatures, phase response, extended high
or low frequency response, extended range, leak testing,
hydrostatic pressure testing, and others. For more
information, contact your local PCB Piezotronics
distributor, sales representative, or factory customer
service representative.
Returning Equipment
If factory repair is required, our representatives will
provide you with a Return Material Authorization (RMA)
number, which we use to reference any information you
have already provided and expedite the repair process.
This number should be clearly marked on the outside of
all returned package(s) and on any packing list(s)
accompanying the shipment.
Contact Information
PCB Piezotronics, Inc.
3425 Walden Ave.
Depew, NY14043 USA
Toll-free: [phone]
24-hour SensorLine: [phone]
General inquiries: in[email protected]
Repair inquiries: [e-mail]
For a complete list of distributors, global offices and sales
representatives, visit our website, www.pcb.com.
Safety Considerations
This product is intended for use by qualified personnel
who recognize shock hazards and are familiar with the
precautions required to avoid injury. While our equipment
is designed with user safety in mind, the protection
provided by the equipment may be impaired if equipment
is used in a manner not specified by this manual.
Discontinue use and contact our 24-Hour Sensorline if:
Assistance is needed to safely operate equipment
Damage is visible or suspected
Equipment fails or malfunctions
For complete equipment ratings, refer to the enclosed
specification sheet for your product.
Definition of Terms and Symbols
The following symbols may be used in this manual:
DANGER
Indicates an immediate hazardous
situation, which, if not avoided, may
result in death or serious injury.

Manual 21354 Rev E
ECN 50523
CAUTION
Refers to hazards that could damage
the instrument.
NOTE
Indicates tips, recommendations and
important information. The notes
simplify processes and contain
additional information on particular
operating steps.
The following symbols may be found on the equipment
described in this manual:
This symbol on the unit indicates that
high voltage may be present. Use
standard safety precautions to avoid
personal contact with this voltage.
This symbol on the unit indicates that
the user should refer to the operating
instructions located in the manual.
This symbol indicates safety, earth
ground.

Manual 21354 Rev E
ECN 50523
PCB工业监视和测量设备 - 中国RoHS2公布表
PCB Industrial Monitoring and Measuring Equipment - China RoHS 2 Disclosure Table
部件名称
有害物质
铅(Pb)
汞
(Hg)
镉
(Cd)
六价铬(Cr(VI))
多溴联苯 (PBB)
多溴二苯醚(PBDE)
住房
O
O
O
O
O
O
PCB板
X
O
O
O
O
O
电气连接器
O
O
O
O
O
O
压电晶体
X
O
O
O
O
O
环氧
O
O
O
O
O
O
铁氟龙
O
O
O
O
O
O
电子
O
O
O
O
O
O
厚膜基板
O
O
X
O
O
O
电线
O
O
O
O
O
O
电缆
X
O
O
O
O
O
塑料
O
O
O
O
O
O
焊接
X
O
O
O
O
O
铜合金/黄铜
X
O
O
O
O
O
本表格依据 SJ/T 11364 的规定编制。
O：表示该有害物质在该部件所有均质材料中的含量均在 GB/T 26572 规定的限量要求以下。
X：表示该有害物质至少在该部件的某一均质材料中的含量超出 GB/T 26572 规定的限量要求。
铅是欧洲RoHS指令2011/65/ EU附件三和附件四目前由于允许的豁免。
CHINA RoHS COMPLIANCE

Manual 21354 Rev E
ECN 50523
Component Name
Hazardous Substances
Lead (Pb)
Mercury (Hg)
Cadmium (Cd)
Chromium VI
Compounds
(Cr(VI))
Polybrominated
Biphenyls (PBB)
Polybrominated
Diphenyl Ethers
(PBDE)
Housing
O
O
O
O
O
O
PCB Board
X
O
O
O
O
O
Electrical Connectors
O
O
O
O
O
O
Piezoelectric Crystals
X
O
O
O
O
O
Epoxy
O
O
O
O
O
O
Teflon
O
O
O
O
O
O
Electronics
O
O
O
O
O
O
Thick Film Substrate
O
O
X
O
O
O
Wires
O
O
O
O
O
O
Cables
X
O
O
O
O
O
Plastic
O
O
O
O
O
O
Solder
X
O
O
O
O
O
Copper Alloy/Brass
X
O
O
O
O
O
This table is prepared in accordance with the provisions of SJ/T 11364.
O: Indicates that said hazardous substance contained in all of the homogeneous materials for this part is below the limit
requirement of GB/T 26572.
X: Indicates that said hazardous substance contained in at least one of the homogeneous materials for this part is above the limit
requirement of GB/T 26572.
Lead is present due to allowed exemption in Annex III or Annex IV of the European RoHS Directive 2011/65/EU.

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
1
TABLE OF CONTENTS
Sections Page
1.0 DESCRIPTION 2
2.0 INSTALLATION 3
3.0 OPERATION 4
4.0 BLOCK DIAGRAM DESCRIPTION 5
5.0 VERIFICATION OF NORMAL OPERATION 7
Figures
1 - 8120 SERIES INSTRUMENT WITH DIGITAL INDICATOR 2
2 - FULL-SCALE DISPLAYS FOR THREE RANGES 4
3 - SCALE, DECIMAL POINT, DUMMY ZERO SWITCHES 4
4 - A/D CONVERTER TIMING DIAGRAM 8
5 - BLOCK DIAGRAM DESCRIPTION 9
Tables
1 - 8120 SERIES MODEL NUMBERING 2
2 - SPECIFICATIONS 3
If you need information regarding specific Model 8120 components and circuitry, please contact the
Force/Torque Division of PCB toll-free at [phone], or e-mail [email protected].
MANUAL NUMBER: 27259
REVISION: NR
ECN:

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
2
1.0 DESCRIPTION
The 8120 Instrument Series is a family of premium
signal conditioning instruments that includes
models to accommodate virtually all types of
transducers and signal sources commonly
encountered in electro-mechanical testing and
control operations. The 8120 Instruments are
available in three forms: Signal Conditioner only;
Signal Conditioner with Digital Indicator; and
Signal Conditioner with Digital Indicator and Hi-Lo
Limits. The Model numbering system used with the
8120 Series identifies the form and the type of
signal source. This numbering system is further
explained in Table 1. From Table 1, it can be seen
that all models having a Digital Indicator are
identified by a -_10A or -_30A suffix, with the first
digit identifying the type of signal source.
The 8120 Series instruction manual system is
designed to provide the user with the following
documentation: (1) a separate instruction manual for
each type of Signal Conditioner purchased; (2) an
instruction manual covering only the Digital
Indicator section of a 8120 Series instrument, but
applicable to any -110A or –130A instrument; and
(3) an instruction manual covering only the Hi-Lo
Limit section 2 of a 8120 Series instrument, but
applicable to any –130A instrument. It is the
purpose of this manual to cover the Digital Indicator
section of all -_10A or -_30A instruments.
The Digital Indicator section of any -_10A or -_30A
instrument consists of a printed circuit board on
which are mounted the required circuit components
for digitizing the analog output of the Signal
Conditioner and the light-emitting-diode (LED)
display. This board is mounted above the circuit
board that contains the components for the Signal
Conditioner. The digits that comprise the display
are mounted on a small board, which is affixed to
the digitizer board with a right-angle printed-circuit
board header. The -_30A instruments contain an
additional printed-circuit board for the Hi-Lo Limit
circuitry.
The LED display is comprised of six orange digits
with polarity sign. The 0.4-inch height of the digits,
combined with the inherent brilliance of an LED
type of display, make the display easily discernible
in normal room lighting. The display is viewed
through the red plastic front panel of the instrument
to provide filtering of external light and enhance the
display brilliance. The front panel is opaque except
for that portion through which the display is
viewed. A typical 8120 Instrument with Digital
Indicator is shown in Figure 1.
Table 1 – 8120 Model Numbering System
8120-_ _0A
First di
g
it after the dash identifies t
y
pe o
f
signal source:
1= Strain Gages (DC excited)
4= Strain Gages (AC excited)
7= Pulse Pick-ups (Frequency)
Second digit after the dash identifies form:
0= signal conditioner only
1= signal conditioner with digital indicator
3 = signal conditioner with digital indicator
and Hi-Lo Limits
Figure 1 - Model 8120-110A
The Digital Indicator scaling is selected with rear-
panel pushbutton switches. Full-scale values of
±5000 counted by 1 ' s , ± 10000 counted by 2's, or
±20000 counted by 5's can be selected. The most

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
3
significant digit (MSD) of the display contains the
polarity sign and is either unlit or lights as a 1 for
displays of 10000 or greater. The least significant
digit (LSD) is a dummy zero which can be turned
ON or left unlit as desired. In addition, decimal-
point position can be selected to give display
readings as follows: 1.XXXX, lX.XXX, 1XX.XX,
1XXX.X, or 1XXXX (no decimal point). Decimal-
point location and dummy zero selection are also
accomplished with rear-panel switches (miniature
slide-switch bank). When the 20000 scale is
selected, the display is digitally limited to read a
maximum number of 19995 since the MSD is either
unlit or reads a "1" for displays of 10000 or greater.
The 5000 and 10000 scales are analog limited to an
overrange of approximately 5600 and 11200,
respectively. An overrange condition on any range
is indicated by a flashing display. The sampling
rate of the display is 3 samples per second. The
Digital Indicator specifications are summarized in
Table 2.
Table 2 - Specifications
Display: Orange LED’s, six digits with polarity sign, 0.4 inch
height. MDS is either unlit or reads a 1 and contains the
polarity sign. LSD is a dummy zero which can be programmed
to be lit or unlit (rear-panel switch).
Scaling: Selectable at rear panel; full-scale values of ±5000
counted by 1's, ± 10000 counted by 2's, or ±20000 counted by
5's.
Decimal Point: Decimal-point location can be selected with
rear panel switches as follows: 1.XXXX, 1X.XXX, 1XX.XX,
1XXX.X, or 1XXXX (no decimal point).
Sampling Rate: 3 samples per second.
Legends: Each instrument supplied with an appropriate
assortment of user-installable rub-on engineering unit legends.
2.0 INSTALLATION
The 8120 Series Instruments can be operated as
bench-top instruments or they can be rack- or panel-
mounted. Dimensions for all three types of
mounting and corresponding mounting instructions
are given in the accompanying Signal Conditioner
Instruction Manual. The following paragraphs
provide the instructions for legend installation, scale
selection, decimal point/dummy zero selection, and
ac power connection.
Legend Installation
A sheet of dry-transfer lettering is supplied with
each instrument to provide the user with a means of
affixing an engineering-unit legend to the front
panel. The sheet contains the common engineering
units encountered in making electro-mechanical
measurements and additional alphanumeric
characters. Space is supplied on the front panel to
affix the desired legend to the right of the display.
To affix the legend to the front panel, press the dry-
transfer sheet firmly against the panel with the
desired legend or character situated in place.
Rubbing the legend or character with a ballpoint
pen will cause the legend to be transferred onto the
panel. The legend can be protected from scratches,
which may occur during calibration/operation of the
instrument by lightly spraying it with Krylon #1306
Workable Fixative.
If it is desired to change a legend, remove the
legend to be replaced by pressing masking tape
against the legend, then pulling off the gummed
tape.
Scale Selection.
Figure 2 shows the full-scale display for the three
selectable scales: ±5000 counted by 1's, ±10000
counted by 2's, and ±20000 counted by 5's. The
figure also indicates the last active digit and the
dummy zero which can be lit for any scale
selection. The first digit of the display contains the
polarity sign and lights as 1 on the 10000 and 20000
scales for values equal to or greater than 10000. On
the 20000 range, because the most significant digit
is either unlit or a 1 and the count is by 5's, the
greatest number which can be displayed is 19995.
Of course, this would be displayed as 199950 if the
dummy zero were lit.
Scale selection is accomplished with the two
pushbutton switches located at the rear panel. The
panel is marked to indicate which switches are
pushed IN or left OUT for the corresponding scale
selection. The switches have a push-push action

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
4
and are illustrated, with the scale selection coding,
in Figure 3. With both switches OUT, the ±5000
range is selected. With the left switch OUT and the
right switch IN, the ±10000 range is selected. With
the left switch IN and the right switch OUT, the
±20000 range is selected.
Figure 2 - Full-Scale Displays for 3 Ranges
Decimal Point/Dummy Zero Selection
Decimal-point location and dummy zero activation
is selected with a rear-panel miniature slide switch
bank. The switch bank is marked on the rear panel
as shown in Figure 3. The decimal-point position
can be fixed at any one of the display locations
indicated on Figure 3. Place any one of slide
switches 1 through 4 ON to light the decimal point
at the desired location. Place slide switch 5 ON if
no decimal point is to be lit. To activate the dummy
zero (digit to the right of last active digit will
continuously light as a zero), place slide switch 6
ON.
Figure 3 - Scale, Decimal Point, Dummy Zero Switches
AC Power Connection
To protect operating personnel, the 8120 Series
Instruments are equipped with a three-conductor
power cord. When the cord is plugged into the
appropriate receptacle, the instrument is grounded.
The offset pin on the power cord is ground. To
maintain the safety ground when operating the
instrument from a two-contact outlet, use a three-
prong to two-prong adaptor and connect the green
pigtail on the adaptor to ground.
To prepare the instrument for operation, connect the
power cable to a 105-135 volt ac, 50-400 Hz power
source. The instrument can use up to 5 watts of
power.
3.0 OPERATION
The only operation required is turning ON/OFF ac
power to the instrument. This is accomplished with
the rear-panel slide switch (see Figure 3). The
display lights immediately when ac power is ON.
NOTE: In all instances, a flashing display indicates
that an overrange condition has occurred, and it is
likely that the Signal Conditioner amplifiers are
being overdriven. The 5000 and 10000 ranges are
analog limited at approximately 5600 and 11200,
and while a number may be displayed, if the display
is flashing an overrange condition has occurred.
Consequently, the displayed value may be invalid.
The 20000 range is digitally limited to 19995.
When an overrange occurs on this range, the display
will flash all zeros.

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
5
4.0 BLOCK DIAGRAM DESCRIPTION
The purpose of this section is to explain how the
Digital Indicator works by using a simplified block
diagram. This section is not intended to provide a
detailed explanation of electronic circuits for
personnel untrained in electronic technology.
However, it provides an adequate overview of
operation for those familiar with basic electronic
circuit operation. Throughout the following, refer
to Figure 5.
Power Supplies
The integrated-circuit chips which comprise the
A/D Converter and the Overrange Comparator are
CMOS circuits which require ±9 volts regulated.
These voltages are supplied from power supplies
contained on the Signal Conditioner circuit board
and are discussed in the Signal Conditioner
Instruction Manual.
The digital part of the A/D Converter, the Bit
Selector, and the various logic gates and inverters
are operated from +5 volts regulated (TTL logic).
The +5 volt supply consists of a three-terminal
Regulator. The unregulated input to the Regulator
is obtained from Signal Conditioner circuit board
(unregulated side of +9 volt supply).
The BCD-to-7-Segment, Decoder, Display Drivers,
and Display LED’s operate from +6 volts
unregulated. Five volts ac is supplied from the
Signal Conditioner circuit board (secondary of
power transformer located on board). Plus 6 volts
unregulated is developed with a Diode Bridge and
Filter located on the Digital Indicator board.
A +2.5 volts precision reference is supplied from a
precision power supply located on the Signal
Conditioner circuit board. This reference is used in
the A/D Converter for digitizing the analog input
signal.
A/D Converter
The A/D Converter is a dual-slope converter which
digitizes the analog input signal using a ratiometric
integrating technique. The analog signal input, a
reference input, and a clock input are applied to the
converter. The measurement cycle is divided into
an Auto-Zero cycle, a Signal Integrate cycle, and a
Reference Integrate cycle. Each cycle has a time
base in which a certain amount of clock pulses
occur. The clock used is a 100-kHz crystal
oscillator. The Auto-Zero cycle is used to bring the
output of the integrator to zero and lasts 10,000
counts. The next cycle is the Signal Integrate cycle
which also lasts 10,000 counts. If the analog input
is zero at the start of the Signal Integrate cycle, the
integrator will see the same voltage that existed in
the previous state. Thus, the integrator output will
not change but will remain stationary during the
entire Signal Integrate cycle. If the analog input is
not equal to zero, an unbalanced condition exists
compared to the Auto-Zero cycle and the integrator
will generate a ramp whose slope is proportional to
the analog input. At the end of this cycle, the sign
of the ramp is determined. If the input signal was
positive, a voltage which is VREF more negative
than during Auto-Zero is applied to the integrator
input. The A/D Converter chip generates the
equivalent of a +Reference or –Reference from the
single +Reference applied. The reference voltage
returns the output of the integrator to zero. The
time, or number of counts, required to do this is
proportional to the input voltage. The Reference
Integrate cycle can be a maximum of 20,000 counts.
The full measurement cycle is then a maximum of
40,000 counts, with the answer to the measurement
being achieved when the reference voltage returns
the integrator output to zero. The full measurement
cycle is shown in Figure 4.
The DIGIT DRIVES are positive-going signals that
last for 200 clock pulses (see Figure 4). The scan
sequence is D5 (MSD), D4, D3, D2, and D1 (last
active digit). The scan is continuous unless an
overrange occurs. Then all DIGIT DRIVES are
blanked from the end of the first scan until the
beginning of the Reference Integrate cycle when D5
will start the scan again. This gives a blinking or
flashing display as a visual indication of overrange.
Because the Digital Indicator has 5000 and 10000
ranges as well as a 20000 range, an analog
Overrange Comparator is used as well as the
inherent overrange capability of the A/D Converter.

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
6
The Overrange Comparator is described in a
following paragraph.
The binary-coded-decimal (BCD) outputs of the
A/D Converter are positive logic signals that go on
simultaneously with the DIGIT DRIVE. Since the
DIGIT DRIVES are blanked for an overrange on
the 20000 scale, the display will flash all zeros
when this condition occurs on this scale.
Input Attenuators/Range Switches
The 5-volt analog signal input (full scale) and the
2.5-volt reference from the Signal Conditioner are
applied to attenuator networks where 2-volt and l-
volt signal and reference inputs are developed for
the A/D Converter. Since, on the 20000 range, the
Reference Integrate cycle can be twice as long as
the Signal Integrate cycle, the analog input voltage
required to give a full-scale reading is exactly equal
to 2 VREF. Consequently, on the 20000 range, the
VREF is 1 volt and the VSIG is 2 volts for full
scale. On the 10000 range, the two cycles can be
equal; thus, VSIG = VREF = 2 volts. On the 5000
range, the analog voltage for a full-scale reading is
then equal to 1/2 VREF; thus, VREF must be 2
volts and VSIG 1 volt. The appropriate levels are
switched to the A/D Converter through the rear-
panel Range switches.
Bit Selector/Decoding Logic
The Bit Selector transfers one of two sets of 4-line
BCD data applied at input ports to output ports
upon receiving a command at the A SELECT or B
SELECT port. When the A SELECT port is high,
the X input data is transferred to the Z output ports.
Conversely, when the B SELECT input is high, the
Y input data is transferred to the Z output ports.
The Y data is obtained directly from the BCD
output ports of the A/D Converter. The X data is
comprised of specially coded bits used to count by
2' s or 5' s when the 10000 or 20000 ranges are
selected, respectively. On the 5000 range, the A
SELECT input is held low through the Range
switches and the B SELECT input is high. The Y
data is transferred to the output of the Bit Selector
and the display count is by 1's. On the 10000 range,
the A SELECT input is held low except when the
Dl DIGIT DRIVE is high. When D1 is high, the A
SELECT is high and the B SELECT is low,
transferring the X data to the Z ports of the Bit
Selector and allowing the display to count by 2's.
Operation on the 20000 range is identical except
that the bit coding is arranged to give a count by 5's
with the X data.
Display Coding/Driving
The display is a 4.5-digit LED display with polarity
and a dummy zero. DS2 through DS6 are 7-
segment displays with common cathodes. The Bit
Selector output ports are connected as inputs to a
BCD-to-7-Segment Decoder. The 7 outputs of the
decoder are connected as inputs to the segments
(anodes) of DS2 through DS6. The DIGIT
DRIVES of the A/D Converter are used to
sequentially turn on DS2 through DS6 through
Display Drivers which sink current. DS1 is either
unlit or lights as a 1 for displays of 10000 or
greater. Unlike DS2 through DS6, DS1 is a
common anode device. The DS1 segments
(cathodes) are sinked via a display driver from the 1
bit of the A/D Converter. The DS1 anode is then
brought high by D5 through a driver comprised of
an inverter and a transistor which applies +6 volts
unregulated to the anode when D5 is high.
The last digit of the Display (DS6) is the dummy
zero digit. When the Dummy Zero Select switch is
ON, the DS6 cathode is sinked when D5 is high.
The outputs of the BCD-to-7-Segment Decoder are
tied to the DS6 segments. Also, when D5 is high,
the B SELECT input to the Bit Selector is pulled
low through the NOR gate connected to the port.
The A SELECT input is also low since it is either
held hard low through the Range switches on the
5000 range or it is connected to D1 through the
Range switches on the 10000 and 20000 ranges
(when D5 is high D1 must be low). With the A
SELECT and B SELECT inputs both low, the Z
ports of the Bit Selector assume the low state no
matter what the X and Y input data reads.
Consequently, each time D5 is high, DS6 displays a
zero.

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
7
The polarity sign is also part of DS1. The minus (-)
segment is always lit through 6 volts and an
external resistor tied to circuit common. When the
A/D Converter senses a positive polarity, the
POLARITY port goes high. This action drives an
inverter low to light the vertical portion of the
polarity sign.
Decimal point position is selected with rear-panel
slide switches (as is dummy zero selection). Only
one of the Decimal slide switches is turned ON at
any one time. The decimal point LED for DS1 is
hard wired to +6 volts. Turning ON the associated
Decimal switch connects an external resistor and
circuit common to the other side of the decimal
point LED. Since the remaining digits with
decimal-point LED’s (DS2 through DS4) are
common cathodes devices, each LED is sinked
when the corresponding DIGIT DRIVE is high and
associated Decimal switch is ON, applying +6 volts
to the other side of the LED through an external
resistor.
Analog Overrange
Digital overrange for the 20000 range is inherent in
the A/D Converter chip and has been previously
described. However, for the 5000 and 10000
ranges, an analog overrange circuit is required. The
Overrange Comparator is dc biased with equal
resistors returned to the ±9 volt supplies so that its
output is at approximately 4.5 volts. Both of the
comparator inputs are connected through diodes to
the analog input from the Signal Conditioner.
When the analog input is one diode drop above or
below the comparator biasing, an overrange
condition exists since approximately 5.2 volts is
present at the analog input (5 volts = full-scale
value). The output of the Overrange Comparator
goes low when either of the input diodes is forward
biased. The comparator output and the BUSY
output of the A/D Converter are gated through an
OR gate. The BUSY signal is high during the
Signal and Reference Integrate cycles of the A/D
Converter, then it goes low. This causes the output
of the OR gate to go low. The BLANK port of the
BCD-to-7-Segment Decoder is normally held high
through an external resistor. When the OR gate
output goes low, the BLANK port is pulled low
through a diode, causing DS2 through DS6 to flash.
Since DS1 is not driven from the decoder, a second
diode and resistor are used to pull the A/D
Converter 1-bit output low when the overrange OR
gate is low. This action causes DS1 to flash.
5.0 VERIFICATION OF
NORMAL OPERATION
It is the purpose of this section to aid the user in
rapidly determining whether the Digital Indicator is
functioning normally or whether it is the source of
the observed trouble. In the event a repair to the
Digital Indicator is required, a complete parts list,
schematic diagram, and component location
drawing are included in this manual. The user may
also contact the factory for assistance.
One of the two techniques can be used to rapidly
determine whether the Digital Indicator is
malfunctioning or whether the problem is in the
Signal Conditioner, transducer, or transducer
cabling. If the unit is a –_10A instrument (no Hi-
Lo Limits), attempt to zero and calibrate the Signal
Conditioner while observing the Signal Conditioner
analog output (use the dc-to-2Hz output) on a dc-
coupled oscilloscope. If the Digital Indicator is
unstable or reads erratically, but the oscilloscope
indicates a stable analog output from the Signal
Conditioner, the problem is likely in the Digital
Indicator. In the event the Signal Conditioner
output is unstable or noisy, consult the Signal
Conditioner Instruction Manual for the proper
action to be taken.
If the instrument is a –_30A type, push one of the
Limit pushbuttons and observe how the limit value
is displayed on the Digital Indicator. If the display
is stable with the Limit button pressed, but is
unstable when the button is released, the problem is
in the Signal Conditioner, transducer, or transducer
cabling. If the display is unstable or erratic whether
the button is pressed or released, the problem is in
the Digital Indicator.

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
8
Figure 4 - A/D Converter Timing Diagram

MODEL 8120 DIGITAL INDICATOR OPTION OPERATION MANUAL
9
Figure 5 - Block Diagram

i
Table of Contents
Section 1.0 Description Page 1
Section 2.0 Installation and Cabling Page 1
Section 3.0 Calibration Page 7
Section 4.0 Calibration of PCB Rotary Transformer Torque Sensors Page 8
Section 5.0 Troubleshooting Page 9
Reference Figures
Figure 1 Bench Mounting Clearance Dimensions Page 2
Figure 2 Panel Mounting Cut-Out Dimensions Page 2
Figure 3 Panel Mount Assembly Page 3
Figure 4 Rack Mounting Dimensions Page 4
Figure 5 4200 Series Cabling Page 5
Figure 6 182-015A Connector Pin-Out Page 5
Figure 7 4-Conductor Cabling Page 5
Figure 8 4100 Series Cabling Page 5
Figure 9 8-Conductor Cabling Page 5
Figure 10 Remote Calibration Methods Page 6
Figure 11 Master / Slave Connections Page 6
Figure 12 Front Panel Descriptions Page 11
Figure 13 Rear Panel Descriptions Page 12
MODEL 8120-400A AC SIGNAL CONDITIONER OPERATION MANUAL
MANUAL NUMBER: 18222
REVISION: B
ECO NUMBER: 37012

MODEL 8120-400A AC SIGNAL CONDITIONER OPERATION MANUAL
1.0 DESCRIPTION
Model 8120-400A Transducer Signal
Conditioner/Amplifier is designed for use with
resistance strain gage transducers that require
an AC excitation-amplification source. It
supplies a 3.28 kHz frequency, precision
amplitude-regulated excitation, which is
remotely sensed to the transducer. The
instrument uses a phase-sensitive carrier
amplifier-demodulator design so that both
direction and magnitude of the applied force are
determined. The 8120-400A contains all
necessary balancing and calibration controls
and condition/amplify the applied input to a
standard ±5 volt DC analog output level. Two
analog outputs, both having low-pass cutoff
frequencies, one of 2 Hz and the other of 400
Hz, are provided. The filtered outputs provide
for averaging of signals containing noise or
other unwanted dynamic components that are
periodic in nature.
The 8120-400A is used in applications
involving transformer coupling of the strain
gage bridge (rotary transformer coupled torque
sensors for example), and in applications that
require a high sensitivity (amplification) with
optimum "signal to noise" characteristics.
Carrier amplifiers offer higher sensitivity than
comparable DC-excited bridge amplifiers, and
since they respond only to the modulated carrier
frequency, they reject certain extraneous
voltages that cause interference with DC-
excited bridge instruments.
Note: If you have a PCB rotary transformer
torque sensor, please refer to Section 3 of this
manual, or to either the 4100 Series Rotary
Transformer Torque Sensor Manual (PCB
Manual #18227), or the 4200 Series Rotary
Transformer Torque Sensor Manual (PCB
Manual #18228), for calibration procedures.
Calibration of the instrument is made through
conventional shunt technique, using an
internally installed calibration resistor, or an
external shunt calibration reference, such as our
Model 8113A or 8113-105A Shunt Calibration
References. Front panel calibration buttons
provide for calibration in both the positive and
negative directions. An internal symmetry
control provides independent adjustment of the
negative direction sensitivity for transducers
that do not have symmetrical positive and
negative slope characteristics. Positive
direction calibration can be checked by means
of REMOTE CAL terminals on the instrument
I/O connector.
The 8120-400A Strain Gage Conditioner is also
available in two additional forms. The 8120-
410A is similar to the 8120-400A except it also
contains a dedicated 4.5 digit LED display with
a 3Hz update rate. The resolution of the digital
display is 1:5000 (0.02% FS). The display also
has a selectable decimal point, trick count
multiplier, and a trailing inert zero. For more
information on instruments with digital display,
refer to PCB Manual #27259. The Model
8120-430A contains a Limit section (in addition
to a Digital Indicator) that provides
High/OK/Low indications and outputs. Refer to
PCB Manual #19479 for more information.
The Digital Indicator and Limit features are
standard to all 8120 Series Instruments.
2.0 INSTALLATION AND CABLING
The following paragraphs provide the
instructions for instrument installation and
cabling.
Mounting
The 8120 Series Instruments can be operated as
bench-top units or they can be rack or panel
mounted. Clearance dimensions for a bench-
mounted instrument are given in Figure 1 and
cut-out dimensions for panel mounting are
shown in Figure 2.
1

MODEL 8120-400A AC SIGNAL CONDITIONER OPERATION MANUAL
Figure 1 – Bench Mounting Clearance Dimensions
Figure 2 – Panel Mounting Cut-Out Dimensions
To panel mount an instrument, proceed as follows, referring to Figure 3.
Important: The unit is shipped with two spacer washers on the securing screws of the rear-panel I/O
connector. When panel-mounting the unit, you must remove these washers so that the printed circuit
board may move forward about 1/8" during Step (6).
1. Remove the front panel by removing the two #2-56 x 3/8” flat-head screws.
2. Remove the front bezel by removing the four #6-32 x 5/8” fillister-head screws.
3. Make the panel cut-out and drill the screw clearance holes indicated in Figure 2. The front
bezel can be used as a template to define the rectangular cut-out and locate the clearance holes.
4. Hold the instrument enclosure behind the panel and re-attach the front bezel to the enclosure
from the front of the panel with the four remaining screws.
5. Reinstall the front panel.
2

MODEL 8120-400A AC SIGNAL CONDITIONER OPERATION MANUAL
6. Tighten the two securing screws of the rear panel I/O connector to ensure that the connector is
seated and that the conditioner printed-circuit board is pushed fully forward so that the front-
panel screwdriver adjustments and buttons are accessible. These screws give approximately 1/8
inch adjustment; consequently, this is the maximum panel thickness that should be used.
Caution: Do not over tighten the connector securing screws or resultant damage may occur to the
printed-circuit board.
8120 SERIES
MODULE
Figure 3 – Panel Mount Assembly
To rack mount an instrument, refer to Figure 4. Up to four 8120 Series Instruments can be mounted in a
19-inch rack using the 1.75-inch high Model 8171A Rack Adaptor.
3

MODEL 8120-400A AC SIGNAL CONDITIONER OPERATION MANUAL
Figure 4 – Rack Mounting Dimensions
AC Power Connection
To protect operating personnel, the 8120 Series
Instruments are equipped with a three-
conductor power cord. When the cord is
plugged into the appropriate receptacle, the
instrument is grounded. The offset pin on the
power cord is ground. To maintain the safety
ground when operating the unit from a two-
contact outlet, use a three-prong to two-prong
adaptor and connect the green pigtail on the
adaptor to ground.
To prepare the instrument for operation,
connect the power cable to a 105-135 volt AC,
50-400 Hz power source. The instrument can
use up to 5 watts of power.
Calibration Resistor
If a fixed resistor is shunted across one arm of a
strain gage Wheatstone Bridge, it produces an
unbalance equivalent to that of a particular
value of mechanical input. If this Equivalent
Input value is accurately known, it can be used
as a reference point for shunt calibration of the
system. Upon completion of installation of the
transducer and its associated cabling, the user
can:
1. Perform an overall dead weight calibration
using a precisely known value of
mechanical input. Shunt calibration data
then can be collected by means of the
installed calibration resistor for
convenience in subsequent checking.
2. Replace the installed calibration resistor
with one (or an equivalent resistance value)
supplied by the transducer manufacturer to
achieve a precisely known Equivalent Input
allowing the instrument sensitivity to be
adjusted correctly.
3. Determine the Equivalent Input value for
the installed calibration resistor, knowing
the transducer sensitivity, and adjust the
instrument sensitivity accordingly.
4. A precision 59KΩcalibration resistor is
installed in the 8120 at the factory. The
installed resistor can usually be used even
though the transducer calibration data
mentions some other resistance value. In
Section 3 of this manual, the techniques
described above are demonstrated. If,
however, the installed value of calibration
resistor is not appropriate for the transducer
and measurement range to be used, the
59KΩresistor should be replaced at this
time. The calibration resistor is mounted
on solder terminals located at the front edge
of the conditioner printed-circuit board in
the instrument. It can be accessed by
removing the front panel.
Note: PCB 4200 Series Rotary Transformer
Torque Transducers are supplied with the
appropriate calibration resistor integral to the
transducer. When this type of transducer is
used with the 8120-400A, it is not necessary to
remove the 59KΩresistor internal to the
instrument. The calibration resistor can be
appropriately connected to the 8120-400A
calibration circuit via the transducer cabling.
Refer to Figure 5 and the following section.
4

MODEL 8120-400A AC SIGNAL CONDITIONER OPERATION MANUAL
Figure 5 – PCB 4200 Series Cabling
Transducer Cabling
Cabling to the transducer is accomplished via
the supplied instrument I/O connector (PCB
Model 182-015A). The I/O connector pin
numbers and functions are given in Figure 6.
Rear View
PIN PIN
1 +EXCITATION A +SENSE
2 -EXCITATION B -SENSE
3 +SIGNAL INPUT C CALIBRATION SENSE
4 - SIGNAL INPUT D OSC. DISABLE
5 SIGNAL COMMON E TRANSDUCER CABLE SHIELD
6 OSC. INPUT F OSC. OUTPUT
7 NC H ANALOG OUTPUT
8 REMOTE CALIBRATION J ANALOG OUTPUT
9 OUTPUT SHIELD K NC
10 OUTPUT SIGNAL COMMON L NC
Figure 6 – 182-015A Pin Out
Transducer cabling should take the form of a 4,
6, or 8-wire cable configuration. The 4-wire
configuration, shown in Figure 7, should be
used when overall deadweight calibration is the
method used and the required cable length is
less than 20 feet.
Figure 7 – 4 Conductor Cabling
The 6-wire configuration, shown in Figure 8,
should be used when the instrument is to be
calibrated by achieving a precisely known
Equivalent Input value through the use of a
shunt calibration resistor supplied by the
transducer manufacturer and when the required
cable length is less than 20 feet.
Figure 8 – PCB 4100 Series Cabling
The 8-wire configuration, shown in Figure 9,
should be used with cable lengths longer than
20 feet since the excitation voltage is sensed
and regulated at the transducer and optimum
shunt calibration can be achieved.
Figure 9 – 8 Conductor Cabling
5