User’s Guide
®
An OMEGA Technologies Company
e-mail:[email protected]
DMD-476 Bridgesensor
AC Powered Signal Conditioner
Description
Specifications
NOTE: Unless otherwise noted, specifications apply after one hour
warm up at 25°C ambient. Temperature coefficients apply between
0°C and 55°C ambient.
The Model DMD-476 is a self contained, AC
powered signal conditioner for bridge type
instrumentation. It contains a precision
instrumentation amplifier with isolated, filtered
outputandahighlyregulated,lownoise,adjustable
output bridge excitation source. The unit is
completely encapsulated for use in rugged
environments.
Isolation
700 VDC
60pF
Input to Output
Amplifier
Gain
Adjustment Range
Input for 4 - 20 mA Output
5 mV to 50 mV
±0.01% of Full Scale
Linearity
Features
Temperature Stability
50 PPM (0.005%/°C)
Input Noise
n Complete Strain Gage
Bridge Signal Conditioner
.1 Hz to 10 Hz
2 V P-P
Tare Adjustment Range
n Isolated 4-20 mA or 0-20 mA Output
-3 mV to +25 mV
(Equals 80% F.S. of
3 mV/V cell)
Bridge Offset
n Output Capable of Driving 1000 ohm Loop
Input Resistance
n Bridge Balance with 80%
Tare Offset Capability
Differential and Common Mode 1000 megohm
Common Mode Rejection, DC
Common Mode Input
Output
100 dB minimum
+ 5 Volts
n High Gain Amplifier; Can Accept Full Scale
Live Load Signals as Low as 5 mV and
Provide 16 mA Output Span
Zero Adjust
0 or 4 mA
Temperature Coefficient
Current Output Span
Compliance Voltage
1mA/ C
4 to 20 mA or 0 to 20 mA
-1 to +20 Volts
n Excitation Supply Capable of Driving
Four Load Cells
-1 mA to +20 mA
0 to 1000 ohms
10 Hertz, 2 Pole Roll Off
Current
n AC Powered
Loop Resistance
Frequency Response, -3dB
n Rugged Epoxy Encapsulated Design
Response Time
Rise Time 10% to 90%
To 0.1% of Final Value
35 ms
100 ms
Applications
Bridge Supply
Voltage Adjustment Range
Temperature Coefficient
Fixed
5 to 10 Volts
n Weighing with Load Cells
n Process Control Add-on Loops
100 PPM Typical
10.2V ±2.5%
Temperature Coefficient
Load Current
60 PPM Typical
0 to 120 mA
n Can Be Used With All Types of
Low Output Sensors
Regulation - Load and Line
Output Noise
0.02% maximum
120 Hz Bandwidth
1 mV RMS, maximum
115 VAC, ±10V 50/60 Hz
@ 7 VA
Power Input
Optional
100, 220 or 230 VAC, –10%
Line Isolation
Capacitance
Dielectric Withstand
Environment
Ambient Operating
Storage
60 pF
1100 Volts RMS
-25°C to +55°C
-25°C to +85°C
18 oz. (510 grams)
Weight
3.75" L x 2.0" W x 2.87" H
(9.53 cm x 5.1 cm x 7.62 cm)
Size
3
MODEL DMD-476 Block Diagram
SWB - Excitation Voltage
Mechanical Specifications
SWB-1
ON
OFF
Excitation Voltage
Fixed 10 Volts
Adjustable
SWA - Control Switch
SWA-1
OFF
Tare Range
-3mV to +15 mV
ON
+15 mV to +25 mV
SWA-2
OFF
Zero Current
4 mA
Terminal Strip Assignments
Screw
ON
0 mA
Screw
Terminal
Function
Function
Terminal
1
2
3
4
5
-SENSE
-EXCITATION
+SENSE
6
7
AC
SWA-4 SWA-5
Span Range
40 mV to 50 mV
20 mV to 40 mV
10 mV to 20 mV
5 mV to 10 mV
+SIGNAL
-SIGNAL
OUTPUT
RETURN
ON
OFF
ON
ON
ON
OFF
OFF
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+EXCITATION
AC
9
10
OFF
4
Getting Started with the Model DMD-476
1. Excitation Supply. If remote sensing is not used, connect +Sense to +Excitation, terminal 3 to 4, and
connect -Sense to -Excitation, terminal 1 to 2.
2. Apply power to the DMD-476 and adjust the Excitation supply. Turn SWB-1 “ON” for a fixed 10 Volts.
This will set the supply to 10.2 ±2.5% and provide the best temperature stability. For voltages between
5 and 10 Volts, place SWB-1 in the “OFF” position and set the Excitation Supply with potentiometer
E. SWB-2 may be in either position.
3. Turn the power to the DMD-476 off and connect the load cell to the DMD-476 Excitation terminals and
the Amplifier Inputs.
4. Turn on power to the DMD-476.
5. Turn SWA-3 “ON”. (To set output ZERO current with pot D.)
6. Select the expected full scale signal range according to the table with SWA-4 and
SWA-5. If the output from the load cell is not known, set both SW-4 and
SW-5 “ON” for the 40-50mV range.
7. Set SWA-2 “OFF” for 4mA or SWA-2 “ON” for 0mA output ZERO.
8. Adjust D potentiometer for desired ZERO current.
9. Turn SWA-3 “OFF”. Expect output current to change.
10. Apply no load or dead weight to load cell.
11. Adjust TARE potentiometers A and B for the same ZERO current set in Step 8.
SWA-1 “OFF” provides a bridge output balance of -3mV to +15mV, and “ON” between +15mV and
+25mV.
12. Apply full scale load and adjust SPAN (GAIN) potentiometer C for the desired full scale output current.
Set Range switches SWA-4 and SWA-5 as required.
13. RemovefullscaleloadandcheckZEROoutputcurrent. AdjustFINETAREpotentiometerAifrequired.
14. Recheck full scale as in Step 12.
15. End.
Note: If the amplifier is used without using the DMD-476 Excitation Supply, the external power supply low
side must be connected to the -EXCITATION terminal 2 on the Model DMD-476, or one of the inputs
must be tied to terminal 2, -EXCITATION. This provides a DC return path for the finite amplifier input
current.
5
Amplifier
The amplifier is a true differential input, low drift Instrumentation Amplifier with less than 100pA input
current. It has a common mode range of 5 Volts with respect to the - EXCITATION supply terminal and
a minimum of 100dB rejection of the common mode voltage. The input amplifier and excitation supply are
DC isolated from the AC line and the current output.
The isolated output current source has a compliance of 20 Volts to allow the Model DMD-476 to operate
with zero to 1000 Ohms of loop resistance.
Tare Weight Compensation
The Model DMD-476 has two different zero controls. One is called the OUTPUT zero and can be set to
0mA or 4mA with SWA-2. The other zero control is called TARE. SWA-1 allows the selection of one of
two TARE ranges, -3mV to 15mV or +15mV to +25mV. Potentiometers are available for COARSE and
FINE TARE adjustments.
Connecting to a Sensor
AnyamplifierhasafiniteinputcurrentwhichmusthaveDCreturnpathtotheamplifierpowersupplies. This
path is automatically provided when the Model DMD-476 Bridge Excitation Supply is used to excite the
sensor. If an external supply is used, one side of the external supply must be connected to the DMD-476
common, Terminal 2. Be sure that the common mode voltage limits are observed. This would generally
limit the external power supply to 10 Volts assuming that half the voltage would be common mode, as is
the case when exciting a full bridge.
When the full scale output of a sensor is measured in millivolts, say 10 millivolts, care must be exercised
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in wiring systems. At 10 millivolts full scale, each microvolt (10 volts) contributes 0.01% of full scale
output. Wire connections can generate microvolts of potential due to contact potentials. These will also
be thermoelectric potentials and thus vary with temperature differences. All wires used in connecting up
the Model DMD-476 should be of the same material. If any intervening connections are made such as a
terminal block, the terminal block connecting points should have good thermal contact so they will always
be at the same temperature and thus cancel each other.
Transducer Excitation
The bridge excitation supply voltage is set by SWB-1 and potentiometer E. Set SWB-1 ON for a fixed 10
Volts. This will provide the best temperature stability. The supply can be adjusted between 5 and 10 Volts
by setting SWB-1 OFF and adjusting potentiometer E. The supply will deliver up to 120mA current at any
voltage setting to power up to four 350 ohm sensors.
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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.
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:
FOR NON-WARRANTY REPAIRS, consult OMEGA
for current repair charges. Have the following
information available BEFORE contacting
OMEGA:
1. Purchase Order number under which the
product was PURCHASED,
1. Purchase Order number to cover the COST
of the repair,
2. Model and serial number of product, and
3. Repair instructions and/or specific problems
relative to the product.
2. Model and serial number of the product
under warranty, 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 1999 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.
©
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Process Measurement and Control?
OMEGA...Of Course!
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HEATERS
þ H eating Cable
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M-3241
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