Omega OM2-165 User guide

TEMPERATURE



Thermocouple, RTD & Thermistor
Probes, Connectors, Panels & Assemblies



Wire: Thermocouple, RTD & Thermistor



Calibrators & Ice Point References



Recorders, Controllers & Process Monitors



Infrared Pyrometers

PRESSURE, STRAIN
AND FORCE



Transducers & Strain Gauges



Load Cells & Pressure Gauges



Displacement Transducers



Instrumentation & Accessories

FLOW/LEVEL



Rotameters, Gas Mass Flowmeters
& Flow Computers



Air Velocity Indicators



Turbine/Paddlewheel Systems



Totalizers & Batch Controllers

pH/CONDUCTIVITY



pH Electrodes, Testers & Accessories



Benchtop/Laboratory Meters



Controllers, Calibrators, Simulators
& Pumps



Industrial pH & Conductivity Equipment

DATA ACQUISITION



Data Acquisition &
Engineering Software



Communications-Based
Acquisition Systems



Plug-in Cards for Apple, IBM
& Compatibles



Datalogging Systems



Recorders, Printers & Plotters

HEATERS



Heating Cable



Cartridge & Strip Heaters



Immersion & Band Heaters



Flexible Heaters



Laboratory Heaters

ENVIRONMENTAL
MONITORING AND CONTROL



Metering & Control Instrumentation



Refractometers



Pumps & Tubing



Air, Soil & Water Monitors



Industrial Water & Wastewater
Treatment



pH, Conductivity & Dissolved
Oxygen Instruments

Where Do I Find Everything I Need for

Process Measurement and Control?

OMEGA…Of Course!

M2092/0199

http://www.omega.com

e-mail: [email protected]

omega.com

®

®

User’s Guide

OM2-165

Strain Gage Bridge Signal

Conditioner

Servicing

North America:

USA:

ISO 9001 Certified

One Omega Drive, Box 4047
Stamford, CT 06907-0047
Tel: [phone]
FAX: [phone]
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976 Bergar
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For immediate technical or

application assistance:

USA and Canada:

Sales Service: 1-800-826-6342 /
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SM

Customer Service: 1-800-622-2378 /
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OMEGAnet®On-Line Service Internet e-mail

http://www.omega.com [email protected]

OMEGA

®

®

WARRANTY/DISCLAIMER

OMEGA ENGINEERING, INC. warrants this unit to be free of defects in materials and
workmanship for a period of

13 months from date of purchase. OMEGA Warranty adds an

additional one (1) month grace period to the normal

one (1) year product warranty to cover

handling and shipping time. This ensures that OMEGA’s customers receive maximum coverage
on each product.

If the unit malfunctions, it must be returned to the factory for evaluation. OMEGA’s Customer
Service Department will issue an Authorized Return (AR) number immediately upon phone or
written request. Upon examination by OMEGA, if the unit is found to be defective, it will be
repaired or replaced at no charge. OMEGA’s WARRANTY does not apply to defects resulting
from any action of the purchaser, including but not limited to mishandling, improper interfacing,
operation outside of design limits, improper repair, or unauthorized modification. This WARRANTY is
VOID if the unit shows evidence of having been tampered with or shows evidence of having been
damaged as a result of excessive corrosion; or current, heat, moisture or vibration; improper
specification; misapplication; misuse or other operating conditions outside of OMEGA’s control.
Components which wear are not warranted, including but not limited to contact points, fuses,
and triacs.

OMEGA is pleased to offer suggestions on the use of its various products. However,
OMEGA neither assumes responsibility for any omissions or errors nor assumes
liability for any damages that result from the use of its products in accordance with
information provided by OMEGA, either verbal or written. OMEGA warrants only that
the parts manufactured by it will be as specified and free of defects. OMEGA MAKES
NO OTHER WARRANTIES OR REPRESENTATIONS OF ANY KIND WHATSOEVER,
EXPRESS OR IMPLIED, EXCEPT THAT OF TITLE, AND ALL IMPLIED WARRANTIES
INCLUDING ANY WARRANTY OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE HEREBY DISCLAIMED. LIMITATION OF LIABILITY: The
remedies of purchaser set forth herein are exclusive, and the total liability of OMEGA
with respect to this order, whether based on contract, warranty, negligence,
indemnification, strict liability or otherwise, shall not exceed the purchase price of
the component upon which liability is based. In no event shall OMEGA be liable for
consequential, incidental or special damages.

CONDITIONS: Equipment sold by OMEGA is not intended to be used, nor shall it be used: (1) as
a “Basic Component” under 10 CFR 21 (NRC), used in or with any nuclear installation or activity;
or (2) in medical applications or used on humans. Should any Product(s) be used in or with any
nuclear installation or activity, medical application, used on humans, or misused in any way,
OMEGA assumes no responsibility as set forth in our basic WARRANTY/ DISCLAIMER language,
and, additionally, purchaser will indemnify OMEGA and hold OMEGA harmless from any
liability or damage whatsoever arising out of the use of the Product(s) in such a manner.

USA

MADE

IN

7 Specifications

NOTES

7-6

It is the policy of OMEGA to comply with all worldwide safety and EMC/EMI regulations that apply. OMEGA is constantly pursuing
certification of its products to the European New Approach Directives. OMEGA will add the CE mark to every appropriate device
upon certification.

The information contained in this document is believed to be correct, but OMEGA Engineering, Inc. accepts no liability for any
errors it contains, and reserves the right to alter specifications without notice.
WARNING: These products are not designed for use in, and should not be used for, patient-connected applications.

Benelux:

Postbus 8034, 1180 LA Amstelveen
The Netherlands
Tel: [phone] FAX: [phone]
Toll Free in Benelux: 0800 0993344
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Czech Republic:

ul. Rude armady 1868, 733 01 Karvina-Hranice
Tel: [phone] FAX: [phone]
Toll Free: 0800-1-66342
e-mail: [email protected]

France:

9, rue Denis Papin, 78190 Trappes
Tel: [phone] FAX: [phone]
Toll Free in France: 0800-4-06342
e-mail: [email protected]

Germany/Austria:

Daimlerstrasse 26, D-75392
Deckenpfronn, Germany
Tel: [phone] FAX: [phone]
Toll Free in Germany: 0130 11 21 66
e-mail: [email protected]

United Kingdom: ISO 9002 Certified

One Omega Drive
River Bend Technology Centre
Northbank, Irlam, Manchester
M44 5EX, United Kingdom
Tel: [phone] FAX: [phone]
Toll Free in United Kingdom: 0800-488-488
e-mail: [email protected]

RETURN REQUESTS / INQUIRIES

Direct all warranty and repair requests/inquiries to the OMEGA Customer Service Department. BEFORE
RETURNING ANY PRODUCT(S) TO OMEGA, PURCHASER MUST OBTAIN AN AUTHORIZED RETURN (AR)
NUMBER FROM OMEGA’S CUSTOMER SERVICE DEPARTMENT (IN ORDER TO AVOID PROCESSING
DELAYS). The assigned AR number should then be marked on the outside of the return package and on any
correspondence.
The purchaser is responsible for shipping charges, freight, insurance and proper packaging to prevent
breakage in transit.

FOR

WARRANTY RETURNS, please have the

following information available BEFORE
contacting OMEGA:

1. Purchase Order number under which the
product was PURCHASED,

2. Model and serial number of the product under
warranty, and

3. Repair instructions and/or specific problems
relative to the product.

FOR NON-WARRANTY REPAIRS,

consult OMEGA
for current repair charges. Have the following
information available BEFORE contacting OMEGA:

1. Purchase Order number to cover the COST

of the repair,

2. Model and serial number of the product, and

3. Repair instructions and/or specific problems

relative to the product.

OMEGA’s policy is to make running changes, not model changes, whenever an improvement is possible. This affords our
customers the latest in technology and engineering.

OMEGA is a registered trademark of OMEGA ENGINEERING, INC.
© Copyright 1998 OMEGA ENGINEERING, INC. All rights reserved. This document may not be copied, photocopied, reproduced,

translated, or reduced to any electronic medium or machine-readable form, in whole or in part, without the prior written consent
of OMEGA ENGINEERING, INC.

Servicing Europe:

NOTE

The carrier will not honor damage claims unless all shipping material
is saved for inspection. After examining and removing contents,
save packing material and carton in event reshipment is necessary.

OM2-165
Stain Gage Bridge Signal Conditioner

Unpacking Information

Remove the Packing List and verify that you have received all
equipment, including the following (quantities in parentheses):

OM2-165 Signal Conditioner (1)

Operator’s Manual (1)
If you have any questions about the shipment, please call the
OMEGA Customer Service Department.

When you receive the shipment, inspect the container and
equipment for signs of damage. Note any evidence of rough
handling in transit. Immediately report any damage to the
shipment agent.

TABLE OF

CONTENTS

i

Figure 7-1 shows the dimensions of the OM2-165
BRIDGESENSOR

.

Specifications 7

Figure 7-1. Dimensions

Figure 7-2 shows the bottom view and dimensions.

Figure 7-2. Bottom View

7-5

Output - Pin 16

High state, max Source Voltage: 16V
Low State, 100mA max. Current: 0.7V max.

Leakage Currentat 16V: 10µsec max.
Response Time, 100mV Overdrive: 70µsec max.
Rise and Fall Time, 2k to 15V: 2µsec max.

Power requirements

Single Supply Operation: 14 to 16V
Dual Supply Operation: ±14 to ±16V
Current with max. Bridge Load

Positive Supply: 130 mA max.
Negative Supply: 2mA max.

Note: Add any comparator output current to positive power supply

requirement.

Environment

Temperature: 0°C to 70°C
Size: 2” x 2” x 0.6”

7 Specifications

7-4

OM2-165

Strain Gage Bridge Signal Conditioner

Page

Chapter 1 Description

Chapter 2 Transducer Excitation - Bridge Supply

Chapter 3 Instrumentation Amplifier

Chapter 4 Output Comparator

Chapter 5 Reference Supply

Chapter 6 Application Information

6.1 Pressure Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1

6.2 Load Cell Weighing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-3

Chapter 7 Specifications

ii

TABLE OF

CONTENTS

1-1

2-1

3-1

4-1

5-1

6-1

7-1

This page is intentionally blank

OM2-165

Stain Gage Bridge Signal Conditioner

TABLE OF

CONTENTS

iii

Bridge Excitation Supply

Adjustment Range: 4 to 10V

Temperature Coefficient: ±0.01%/°C max.
Output Current, at 4V: 47mA max.

at 10V (See Figure 2-1): 100mA max.

Noise Voltage, dc to 10k Hz: 1 mV

rms’

max.
Load Regulation, 0 to max. load: 0.01%, max.
Power Supply Sensitivity: 1mV/V max.
Output Impedance, at dc: 0.05 ohm typ.

at 100k Hz: 5Ω typ.

Comparator

Trip Point Range

Dual Supply: -10 to 10V
Single Supply: 50mV to 10V
Temperature Coefficient: ±10µV/°C max.

Hysteresis

Dual Supply: 8 mV max. at dc
Single Supply: 4 mV max. at dc

7-3

Specifications 7

Output

Single Supply Operation

(2kΩ min. load to common): 0.05V to 10V

Dual Supply Operation: -10V to 10V.

Minimum Load Resistance: 2kΩ
Frequency Response, Gain = 100 10k Hz
Full power Bandwidth, Gain = 100,

with 2k or greater load: 2k Hz

Reference Supply

+VR: 10.3V, ±0.03V

Temperature Coefficient: ±0.01%/°C max.

Output Impedance, at dc: 0.05Ω

at 100k Hz: 10Ω

Load Current: 5mA max.
+5V Reference: 5V at ± 1%

Output Impedance, to 100k Hz: 1.3kΩ
±0.05V Reference: 0.05V ±2%

Output Impedance, to 100k Hz: 25Ω

7 Specifications

7-2

The OM2-165 BRIDGESENSOR is a complete signal conditioning
system designed for use with RTD’s, transducer bridge circuits,
thermocouples, and other signal sources. It provides power to
excite a strain gage or other type of bridge signal. In addition, a
sensitive comparator is included that can be connected to monitor
the amplifier output. The comparator drives an output switch that
can be used to operate a relay, light or audible alarm.

The OM2-165 also includes a stable voltage reference source which
is then available as a comparator trip point reference or for use as
an output offset voltage for the amplifier. When used in an
instrumentation system, external adjustment pots are frequently
required. For this reason, a complete printed circuit mounting kit
is available which furnishes all the necessary pots as well as test
points and jumpers to alter the operational mode. The mounting
kit plugs into a 15 pin card edge connector that comes with the
mounting kit.

A complete instrumentation or control system can be built using
the OM2-165, a power source, and a transducer. The power source
can be either single or dual polarity.

1

Description

1-1

1 Description

1-2

Instrumentation Amplifier

Gain Range, adjustable: 10 to 1000
Gain Non-linearity: ±0.01%
Gain Temperature Coefficient: ±50pp/°C
Input Resistance

Differential: 10MΩ
Common Mode: 500MΩ

Common Mode Voltage

Single Supply Operation: 2V to 7V
Dual Supply Operation: -7V to 7V

CMRR, dc to 100 Hz, G = 100: 100db, min.

1 kHz 80db, typ.

Input Offset Voltage (adjustable): ±2mV max.

Temperature Coefficient: 5µV/°C max.
Power Supply Sensitivity: 50µV/V max.

Input Bias Current: 70nA max.

Temperature Coefficient: 1nA/°C max.
Differential: ±10nA max.

7

Specifications

7-1

6 Application Information

A good example would be a load cell used in a weighing system. It
is also necessary to use a single polarity power supply. In this case
the bridge power supply and input offset are adjusted as before.
The output however is offset to +5.0 Vdc by using the reference
supply and the output offset pin. Negative loads cause the output
voltage to drop below 5.0 volts and positive load is greater than 5.0
volts. In the example shown in Figure 6-2, the comparator is not
used but could easily be connected to provide a switch closure at
any load in the range.

6-4

Figure 1-2 shows the schematic for the MK-165 mounting kit
with an OM2-165 module installed.

Description 1

1-3

1 Description

1-4

Table 1-1 shows the pin assignment for the OM2-165
BRIDGESENOR

As can be seen, the need for using the separate sense lines depends
entirely on the amount of lead resistance between the bridge power
supply and the itself.

Application Information 6

6-3

Figure 6-2
shows a simi­lar application
except here it
is required to
observe plus
and minus
changes about
an equilibri­um balance
point for the
bridge.

6 Application Information

The bridge voltage has been adjusted for 10 Volts giving a full
scale pressure output of 30 mV from the bridge for 3000 PSI. The
gain of the amplifier has been set at 333.33 so that a 0 to 3000 PSI
pressure change is represented as a 10 Volt output change. The
power supply is a single +15Vdc so the -15V pin has been jumped
to common. The common mode voltage for the amplifier input is
+5 Volts and is thus within the range specified. The circuit is to trip
at 2000 PSI and sound an alarm. The output of the amplifier has
been offset to 50mV so that zero PSI corresponds to 50mV and
30000 PSI is +10.050 volts. Therefore, 2000 PSI is (333.333) x (0.020)
+50mV = 6.7166 V. The comparator setpoint is adjusted for this
value. Latching has been incorporated through a push button
switch which allows for reset after the pressure drops below 2000
PSI.

This example also serves to illustrate the use of the bridge power
supply sensing wires. The transducer is located a significant
distance away from the OM2-165 so there is a noticeable resistance
in the lead wires of 10 ohms. If the sense wires were connected to
Vb right at the module, the actual voltage across the bridge would
be 28.38mV full scale instead of 30mV. Connecting the sense wires
directly across the bridge eliminates the problem entirely.

6-2

Table 1-3 shows the pin assignment for the OM2-165
BRIDGESENOR and potentiometer designations.

Description 1

1-5

1 Description

NOTES

1-6

6

Application Information

6-1

6.1 Pressure Transducer

Figure 6-1 shows a typical application using a standard
350 Ω pressure transducer bridge circuit.

5

NOTES

5-2

The Bridge Supply is variable from +4 to +10 volts and is short
circuit protected for momentary shorts to common. It has two
limits. A maximum current of 100 mA and maximum dissipation
of the output transistor. The Bridge Supply Maximum Load
curves, shown in Figure 2-1, show the maximum load current and
the smallest load resistance as a function of the bridge supply
output voltage.

2

Transducer Excitation - Bridge Supply

2-1

If a Sensor has a lower residence than allowed by the resistance
curve, a series resistor can be added to the bridge supply output,
pin 4. The bridge supply + sense, pin 14 is connected directly to the
sensor since that is the voltage to regulate. See Figure 2-2. The
resistor, RS can be determined from the following equation:

2 Transducer Excitation - Bridge Supply

2-2

where RB is
the sensor
resistance
and VB is
desired
sensor
excitation
voltage.

RS = RB (10 - VB)/VB

The reference power supply uses a very stable zener reference
diode as the primary reference voltage. This voltage is then
converted to three values for use as excitation power supply
voltage adjust, comparator setpoint adjust and amplifier output
offset. The three voltages are +10.3V, +.05V, and +50mV. When the
OM2-165 is used with a single polarity power supply the amplifier
output will not swing to ground potential but it can go to a little
below 50mV. By applying 50mV to the output offset input, a zero
signal to the amplifier becomes equal to 50mV at output. The
amplifier may then swing to a positive value to represent an
increasing input signal. If it is desired to observe both increasing
and decreasing signal changes with a single polarity power supply
it then becomes necessary to make the zero signal level in between
50mV and 10 volts such as 5.0 volts. The 5.0 volt reference voltage
is therefore connected to the output offset. This offsets the
amplifier output to +5.0 volts for zero input signal.

5

Reference Supply

5-1

4 Output Comparator

An internal diode latch circuit is also included in the comparator.
By connecting pin 18 to 20, the comparator will latch in the switch
ON state when the input becomes more positive than the setpoint.
It will not unlatch after the input signal decreases unless the
connection from pin 18 to 20 is opened momentarily or module
power is removed momentarily.

4-2

Transducer Excitation - Bridge Supply 2

An example is illustrated in Figure 2-2, RTD Application. A
standard Platinum RTD with a 0° resistance of 50 ohms and an
alpha of 0.00385 is used. It desired to have an output of +10 volts
for +100° and to measure temperatures between -20 and +100°C,
with zero volts out at 0°. The OM2-165 is operated with dual 15
volt supplies. The comparator is connected to monitor the
amplifier output and the setpoint, pin 19, is connected to a
potentiometer that is connected between the + and -15 Volts
supplies. This allows setting the comparator to any temperature in
the measurement range. The comparator output is connected as an
emitter follower, driving the load positive when the amplifier
output exceeds the setpoint. The comparator output could be used
to drive a dc controlled solid state relay, for example.

The series resistor, RSA is determined as follows:

Sensor Resistance =50 ohms
Sensor Voltage = 4 volts at 80 mA

The Bridge Supply Maximum Load curves show a maximum cur­rent of 47 mA and a minimum resistance of 85 ohms at 4 Volts.

RS = 50 (10-4)/4 = 75 ohms

2-3

The power in RS = I x I x RS = 0.08 x 0.08 x 75 = 0.48 Watt Use a
1 Watt resistor.

Pin 14 will be at 10 volts when the voltage across the 50 ohm
bridge is set to 4 volts. Do not bypass the sensor with a capacitor.

At 0° the bridge will be balanced and the amplifier output will be
zero. Atr + 100° the resistance of the RTD will be 69.25 ohms
producing a voltage of +1.677 volts at the amplifier negative input.
The gain required for 10 Volts output is then 10/(2.0 -1.677) =

30.96, which is set by the potentiometer between pins 26 and 27.
At -20°, the RTD resistance will be 46.15 ohms, giving a voltage of
+2.080 at the amplifier negative input. The output voltage will be

30.96 (-0.08) = -2.48 volts.

The error due to the OM2-165 typical 0.5mV input offset is

30.96 x .5

-3

= 15.4mV, or about 0.15°, and the input offset, pin 22,
can be left open. Do not connect pin 22 to any voltage when it is
desired not to adjust the input offset.

2 Transducer Excitation - Bridge Supply

2-4

The comparator is designed to monitor the output of the
instrumentation amplifier and provide a solid state switch closure
when the amplifier voltage reaches a pre-set level. The pre-set level
is determined by a potentiometer adjusted voltage which is fed
into the set input of the comparator. For a precise and stable
setpoint, the OM2-165 provides a very stable 10.3 volt reference
voltage that can be used as a source for the setpoint.

If the set input is more positive than the comparator input, the
output switch will be OFF, and of course the reverse is also true.
The output switch is an open collector NPN transistor and will
source or sink up to 100 mA. The switch is current limited so that it
cannot be damaged by trying to drive too small a load resistance.
However, if the collector of the transistor is connected directly to a
positive supply such as +15 Vdc and the emitter is grounded, the
transistor would have to dissipate over 2 watts if turned on and
would fail after a short time. Use caution when connecting load
circuits.

4

Output Comparator

4-1

3 Specifications

NOTES

3-4

3-1

The built-in amplifier is true differential input, low drift,
instrumentation amplifier. It is factory trimmed for a high common
mode rejection ratio (CMRR) and external adjustments for input
and output offsets. See Figure 3-1.

3

Instrumentation Amplifier

Figure 3-1. Common Mode Rejection Ratio Graph

The minimum gain is 10 and maximum gain is 1000. Gain is set be
one resistor, Rg, connected across pin 26 and 27. RG can be
determined to within 2% from the following formula, for gain A:

Rg = [2.02

5

/A) - 200]/[1 - 10/A]

In most applications it is best to split the gain resistor into two
potentiometers to provide a course and a fine adjustment. Gain
resistors should have low temperature coefficient.

The input offset is the output voltage divided by the amplifier
gain. For example, if the gain is 500 and the output voltage is 0.5
Volt, the input offset is 1 mV. The input offset is measured and
adjusted by shorting the two inputs together and connecting them
to common. The output offset, pin 30, must be connected to pin 3
for no output offset. The input offset is then adjusted for zero
output.

If a single +15 Volt supply is used, the input must have a common
mode voltage between +2 and +7 volts. The output offset must be
set to +50 mV or greater. The output offset is applied to pin 30 and
is not amplified by the gain of the amplifier. The output of the
amplifier should be loaded by connecting a 2000 ohm resistor from
pin 23 to pin 12, amp common. Connect the 50 mV reference,

3 Instrumentation Amplifier

3-2

pin 29, to pin 31, for this adjustment. Measure the voltage between
pin 30 and the amplifier output, pin 23, and adjust the input offset
for zero volts.

The output offset appears at the amplifier output unaltered by the
amplifier gain. This useful feature allows the output to be
purposely offset when using a single power supply or to add
corrective voltages such as thermocouple cold junction
compensation or tare weight. The output offset is buffered by a
high input impedance amplifier with a typical input current of 15
nanoamps.

The amplifier output swings from +50 mV to at least +10.05 volts
when operated from a single +15 volts supply and loaded with a
2k resistor. When operated from dual 15 volt supplies, the output
will swing a minimum of ±10 Volts into a 2 k Load. The output is
protected against shorts to the power supply common.

3-3

Instrumentation Amplifier 3