Omega Products PX726A Installation Manual
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PX726A
Industrial Pressure Transmitter
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An OMEGA Technologies CompanyAn OMEGA Technologies Company
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Operator's Manual
Operator's Manual
M-3601/1101
M-3601/1101
Remove the Packing List and verify that you have received all equipment, including the following
(quantities in parentheses):
PX725A Gauge Pressure Transmitter (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 shipping agent.
M-3601
GAUGE PRESSURE TRANSMITTERS - SERIES PX726
TABLE OF CONTENTS
SECTION TITLE PAGE #
Section 1 - INTRODUCTION
1.1 PRODUCT DESCRIPTION............................................................................................1-1
1.2 TRANSMITTER FEATURES.........................................................................................1-1
1.3 MODELS APPROVED FOR HAZARDOUS AREAS...................................................1-2
1.4 USING THIS MANUAL.................................................................................................1-3
Section 1A - GAUGE PRESSURE TRANSMITTERS series PX726A
1A.1 PRODUCT DESCRIPTION.........................................................................................1A-1
1A.2 THEORY OF OPERATION.........................................................................................1A-2
1A.3 IDENTIFYING TRANSMITTER OPTIONS..............................................................1A-3
1A.4 TRANSMITTER MOUNTING....................................................................................1A-3
Connection-Supported Mounting................................................................................1A-3
Optional Mounting Bracket.........................................................................................1A-4
1A.4.1 Transmitter Housing Rotation....................................................................................1A-4
1A.5 PRESSURE MEASUREMENT APPLICATIONS......................................................1A-6
Liquid Application........................................................................................................1A-6
Gas Application............................................................................................................1A-6
Steam Application........................................................................................................1A-7
Liquid Level Application .............................................................................................1A-8
1A.6 SERVICE CHECKS.....................................................................................................1A-9
1A.7 GP TRANSMITTER SPECIFICATIONS ...................................................................1A-9
Section 2 - INSTALLATION
2.1 INSTALLATION NOTES...............................................................................................2-1
2.2 INSTALLATION IN HAZARDOUS AREAS.................................................................2-1
2.3 ELECTRICAL WIRING NOTES ...................................................................................2-2
2.4 WIRING OF 4-20mA SIGNAL/POWER LOOP.............................................................2-3
2.5 WIRING OF 1-5V SIGNAL/POWER LOOP..................................................................2-6
2.6 EFFECTS OF LEAD & LOAD RESISTANCE & SUPPLY VOLTAGE.......................2-6
Section 3 - CALIBRATION
3.1 CALIBRATION SETUP..................................................................................................3-1
3.2 ACCESS TO ADJUSTMENTS.......................................................................................3-1
3.3 EXTERNAL CHECK PROCEDURE .............................................................................3-4
3.4 CALIBRATION ADJUSTMENTS .................................................................................3-4
3.5 TYPES OF RANGE CALIBRATION.............................................................................3-5
3.6 ZERO-BASED CALIBRATION......................................................................................3-8
3.7 ELEVATED ZERO CALIBRATION ..............................................................................3-8
3.7.1 Zero Elevation Example .................................................................................................3-9
3.8 SUPPRESSED ZERO CALIBRATION..........................................................................3-9
3.8.1 Zero Suppression Example...........................................................................................3-11
3.9 SELECTABLE DAMPING...........................................................................................3-11
M-3601 Contents / 0 - 1
M-3601
GAUGE PRESSURE TRANSMITTERS - SERIES PX726A
TABLE OF CONTENTS
SECTION TITLE PAGE #
Section 4 - SERVICE
4.1 GENERAL.......................................................................................................................4-1
4.2 TROUBLESHOOTING...................................................................................................4-1
4.3 FACTORY REPAIRS......................................................................................................4-1
Section 5 - SPECIFICATIONS
5.1 FUNCTIONAL SPECIFICATIONS...............................................................................5-1
Current Loop Mode: .................................................................................................5-1
Voltage Mode: ...........................................................................................................5-1
Calibration Adjustments:.........................................................................................5-1
Response Time & Damping......................................................................................5-1
Linearity:...................................................................................................................5-2
5.2 PERFORMANCE SPECIFICATION.............................................................................5-2
Accuracy:...................................................................................................................5-2
Resolution: ................................................................................................................5-2
Long Term Stability: ................................................................................................5-2
Ambient Temperature Effect:..................................................................................5-2
Power Supply Effect:................................................................................................5-2
Ripple and Noise:......................................................................................................5-2
5.3 ENVIRONMENTAL SPECIFICATION ........................................................................5-2
Temperature Limits: ................................................................................................5-2
Humidity Limits:......................................................................................................5-3
EMI Effect:................................................................................................................5-3
Surge Protection:......................................................................................................5-3
Vibration Effect: .......................................................................................................5-3
5.4 PHYSICAL SPECIFICATIONS.....................................................................................5-3
Fill Media..................................................................................................................5-3
Electrical Housing....................................................................................................5-3
Electrical Connections:.............................................................................................5-3
APPENDICES
Class I, Division 2 Hazardous Locations .................................................................................. Appendix A
Loop Powered Indicator Option ................................................................................................ Appendix B
Material Safety Data Sheets ......................................................................................................Appendix Z
0 - 2 / Contents M-3601
Section 1
INTRODUCTION
1.1 PRODUCT DESCRIPTION
Series PX726A Gauge Pressure Transmitters (with flush diaphragm) convert pressure
measurements into a proportional 4-20 mA or a 1 - 5 Vdc output signal that functions as the
input to a controller, recorder, indicator or similar device. These transmitters find
application in the gas, water, and process industries that require accurate measurements
over a wide range of environmental conditions.
1.2 TRANSMITTER FEATURES
The features that follow are common to all transmitter models are described in the following
listing:.
E Pressure Sensor. Strain gauge, piezo-resistive sensors perform pressure
measurements.
E Signal-Power Loop. The transmitter requires a nominal 24 Vdc power source to
operate the signal loop, a 2- wire 4-20 mA output.
E Available Voltage Output. For low power applications, a 1-5 Vdc output is user
configurable via an internal jumper.
E Adjustable Ranges. Transmitters are provided with coarse switch and fine pot
adjustments for range calibration. Span is adjustable from 16 to 100% of the upper range
limit, while zero is adjustable from -600 to 600% of the lower range limit for elevation
and suppression.
E Damping. A circuit jumper selects damping periods of .275 sec or 1 ms to control
transmitter response to a change of the measured variable.
E Mechanical Assembly. The transmitter electronics enclosure is constructed of cast
aluminum with an epoxy finish. The materials offered for diaphragms, process
connections, flanges, bolts, etc. are given in Section 1A.
E Fill System. The transmitter's diaphragm and sensor operate in a sealed fluid system.
These systems are furnished with DC 200 as the fill fluid.
E Electrical Conduit Port. Two 1/2 inch NPT female ports are provided for electrical
conduit.
M-3601 Introduction / 1-1
Figure 1-1 – PX726A Gauge Pressure Transmitter (with Internal Diaphragm)
1.3 MODELS APPROVED FOR HAZARDOUS AREAS
Transmitter mode l s ce rti fi e d fo r operation in h a za rdo us areas by Un de rwri ters Laborato ri e s
(UL) will have the appropriate logo inscribed on the instrument data plate. These models
are intended for use in t he following hazardous locations:
1-2 / Introduction M-3601
Explosion-proof for Class I, Division 1, Groups C and D.
Nonincendive for Class I, Division 2, Groups A, B, C and D.
The National Electric Code, Article 500, defines the above classes and divisions as follows:
Class I Atmospheres: Contains flammable gases or vapors.
Class II Atmospheres: Contains combustible dust particles.
Class III Atmospheres: Contains ignitable fibers or flyings.
Division 1:
Where continuous expo su re, o r th reat o f fire o r ex plo sio n m ay b e presen t d u e to accid en t o r
uncommon occurrence.
Division 2:
Where threat of fire or explosion is not normally present, and not likely to result from
abnormal occurrence.
Groups A through D:
Cover various flammable gases an d liquids such as ethyl- ether vapor, gasoline, acetone,
etc.
Groups E through G:
Cover various combustible dusts such as dust fro m metalw o rk in g , co al, co k e carb o n b lack ,
grain, etc.
1.4 USING THIS MANUAL
Section 1A provides information relevant to product description, types of mounting,
measurement applications, service checks, and specificat ions.
Sections 2 through 5 describe installation, calibration, service and general specifications.
The Loop Powered Indicator option is covered in Appendix B.
M-3601 Introduction / 1-3
Section 1A
GAUGE PRESSURE TRANSMITTERS
Series PX726A
1A.1 PRODUCT DESCRIPTION
Gauge Pressure Transmitters convert a pressure measurement into a proportional 4-20 mA
or a 1-5 Vdc outpu t si g n a l th a t ca n b e a ppl i e d to th e input of a co n tro l l er, recorder, i n di ca to r
or similar device. The Series PX726A, shown in Figure 1A-1, provides a standard 1-inch
flush diaphragm press ure connection.
Series PX726A Transmitters are offered in ranges from 0-100 inH
(max.). A listing of r anges for the Series PX726A is given in Table 1A-A.
Because of its compact size and light weight, the transmitter may be installed directly on a
process pipe. For installations that require other mounting arrangements, the transmitter
may be specified with a universal bracket. This bracket can be used to clamp the unit to a
two-inch pipe or secure it to a support structure.
O (max.) to 0-5000 psi
2
Figure 1A-1 - PX726A Gauge Pressure Transmitter (with Internal Diaphragm)
M-3601 GP Transmitters / 1A-1
1A.2 THEORY OF OPERATION
The transmitter body is composed of an electronics housing and a sensor module assembly
as shown in the block diagram Figure 1A-2. The electronics housing contains the amplifier
circuitry and the field wiring terminals. The sensor module contains a pressure input
chamber, a fluid chamber, a recessed isolation diaphragm, and a micro diaphragm that
includes electronic sensing circuitry. (Transmitters with flush diaphragms omit the pressure
chamber and have the isolation diap hragm positioned at the very end of the sensor module.)
The input pressure applied to the pressure chamber is hydraulically transmitted through
the fill fluid contained by the isolation diaphragm. This pressure produces a strain on the
silicon diaphragm.
The micro diaphragm assembly contains four piezo-type, strain gauge resistors that are ionimplanted on the diaphragm's s urface and wired in a bridge configuration. The flexing of the
diaphragm causes changes of resistance in the bridge.
The bridge is powered by a constant current supply and produces a millivolt signal that corresponds to the me asured pressure. A circuit associ ated with the bri dge circuitry provides
measurement stability by compens ating for changes of ambient temperature.
The millivolt signal developed by the bridge is applied to a high-gain, linear amplifier and
converted to a tw o-wire, 4-20 m A current output. F igure 1A-2 sho ws this outpu t wired to a
typical external loop circuit that uses a 250-ohm load resistor and a 24 Vdc power source.
Figure 1A-2 - Simplified Diagram of GP Transmitters
1A-2 / GP Transmitters M-3601
The 4-20 mA current flowing through the resistor provides a 1-5 Vdc input for the external
device.
The amplifie r circuit contains gain and o ffset adjustments for setting range calibration. A
jumper selects the damping op tion.
The unit may also be converted, at the users option, to a three-wire 1-5 Vdc output through
jumper selection.
1A.3 IDENTIFYING TRANSMITTER OPTIONS
A data plate affixed to the transmitter body lists the model number, serial number, and
instrument range. To identify the features and options furnished with your model, refer to
the complete model number contained in the sales order. This n umber includes a sequence
of suffix numbers that are identified in Tables 1A-A.
TABLE 1A-A - MODEL NUMBER BREAKDOWN FOR SERIES PX726A
PX726A - (1) – (2) ßßßß (see Codes below)
(1) INPUT RANGE (2) OPTIONS
CODE RANGE
CODE DESCRIPTION
100WCGI 0-17 to 0-100 inH
300WCGI 0-50 to 0-300 inH
400WCGI 0-67 to 0-400 inH
025GI 0-4 to 0-25 psi
050GI 0-8 to 0-50 psi
100GI 0-17 to 0-100 psi
300GI 0-50 to 0-300 psi
500GI 0-83 to 0-500 psi
1KGI 0-167 to 0-1000 psi
3KGI 0-500 to 0-3000 psi
2
2
2
MB Mounting bracket
O
M Local digital indicator
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1A.4 TRANSMITTER MOUNTING
The transmitter may be mounted in any position. However, when it leaves the factory it is
calibrated for operation in the upright position with the electronics enclosure at the top and
the process connection at the bottom as shown in Figure 1A-1. If it is installed in a different
position, the transmitter may require a slight zero adjustment. This procedure is described
in Section 3 - Calibration.
The transmitter may be installed using connection-supported mounting or the optional
mounting bracket as follows:
Connection-Suppo rted Mounting. The tra nsmitter provides a m ale pressure connection
(1-inch NPT) which can also be used for mounting purposes (Figure 1A-4). This method of
mounting allows the transmitter to be connected directly to the pressure pipe or a pipe
fixture. If connection-supported mounting is not feasible, the optional mounting bracket
should be considered.
M-3601 GP Transmitters / 1A-3
Optional Mounting Bracket. The brackets shown in Figure 1A-4 can be used when connection-supported mounting is not feasible or it is desired to mount the transmitter away
from the process. This bracket permits the transmitter to be clamped to a standard 2-inch
pipe with a single 2-1/4 inch u-bolt. The bracket may be positioned on the transmitter to
accommodate either a vert ical or horizontal running pipe.
1A.4.1 Transmitter Housing Rotation
Once mounted, the Transmitter Housing can be rotated up to 180° in either direction, i.e.,
clockwise or counterclockwise. The Transmitter Housing must not be rotated from its
shipped position any more than 180° clockwise or counterclockwise. CAUTION: Trans-
mitter will be damaged if the Trans mitter Housing is rotated more than 180° from
its shipped position.
To rotate the T ransmitte r Housin g, the set scre w that lock s the Pressu re Tran sducer to the
Transmitter Housing must be removed with a 3mm Hex Wrench. Once the Transmitter
Housing has been turned to the desired position, be sure to replace and tighten the set
screw (see Figure 1A-3).
Figure 1A-3 -Transmitter Housing Rotation Diagram
1A-4 / GP Transmitters M-3601
Figure 1A-4 - Overall Dimensions - Model PX726A
(With Neck Type Mounting Bracket)
M-3601 GP Transmitters / 1A-5
1A.5 PRESSURE MEASUREMENT APPLICATIONS
The PX726A transmitter measures the pressure of a process medium flowing through a pipe
or contained in a tank. A discussion of some basic applications follows:
Figure 1A-5 - Process Pipe Mounting
Liquid Application. When measuring pressurized liquids in a process pipe, the
transmitter may be attached to the process line using a valve fixture as shown in Figure 1A-
5. However, if temperature or vibration characteristics at the site exceed the specified limits
of the transmitter, the transmitter should be placed in a more hospitable location with a
connection made through appropriate pressure tubing as shown in Figure 1A-6. Both
arrangements should include shutoff and drain valves to purge connection lines and the
transmitter.
Gas Application. The gas industry typically measures differential pressure, static pressure
and other variables associated with gas flow. A gas installation could use a GP Transmitter
to monitor the static pre ssure an d a DP T ransm itter to me asu re the di ffere ntia l pressu re as
shown below.
Figure 1A-7 sh ows the transmitters conn ected to a horizontal pipe. For these install ations
both transmitters are physically mounted above the connecting line to allow internal
moisture to drain away.
In Figure 1A-8, the gas flow is in a downward direction to minimize the accumulation of
moisture above the orifice plate. Otherwise, both transmitters are mounted and connected
in the same manner as described for horizontal pipes.
Figure 1A-6 - Pipe Tap Connection
Gas installations should include shutoffs and union fittings for both transmitters so that
they can be disconnected from the line without disrupting the process.
1A-6 / GP Transmitters M-3601
Figure 1A-7 - Horizontal Gas Run
Figure 1A-8 - Vertical Gas Run
Steam Application. When measuring steam pressure, the maximum temperature of the
transmitter's electronic circuitry must be strictly observed. Temperatures above the
specified limit (see Environmental Temperature under topic 2.1) will cause output errors and
possibly result in dama ge to the transmitter. One method of prote cting the transmi tter can
be achieved by installing an extended, liquid-filled connecting line as shown in Figures 1A-9
and 1A-10. The liquid functions as a buffer and prevents live steam from entering the
transmitter.
When using liquid-filled system, the connecting line must be installed in a descending step
so that the transmitter is below the level of the process pipe tap and filling tee; this slope
will maintain the liquid in the connecting line and prevent it from being drawn into the
process pipe. Liquid-filled lines must also be properly filled and bled, and checked on a
regular basis.
A liquid-filled line is one way to isolate the transmitter from a steam process. As an
alternate method, a steam trap may be installed in the connecting line. Several
manufacturers offer traps for this application.
Figure 1A-9 - Horizontal Steam Pipe Figure 1A-10 - Vertical Steam Pipe
M-3601 GP Transmitters / 1A-7
Liquid Level Application. GP Transmitters can be used to measure the head pressure of
a column of liquid in an open tank. For this application the transmitter is connected at the
bottom of the tank as shown in Figure 1A-11 (the transmitter co uld also be attached to the
tank through an appropr iate fitting).
The transmitter may be installed at, below, or above the 0% liquid level of the tank. If the
transmitter is exactly at the 0% level, it may be calibrated directly to the zero-base level. If
it is installed below or above the 0% level, a head error will occur. This error must added to
the measuring range during calibration otherwise the transmitter output reading will have
an offset error. Section 3 - Ca libration provides details for zero-based, elevated zero, and
suppressed zero calibration.
Figure 1A-11 - Liquid Leve l - Open Tank
1A-8 / GP Transmitters M-3601
1A.6 SERVICE CHECKS
General troubleshooting hints are listed in Table 1A-B. Some of these checks will require a
digital multimeter (DMM). The DMM may be connected across the (+) and (V) terminals to
measure current directly without opening the current loop. See Section 4 Service for details.
TABLE 1A-B - TROUBLESHOOTING CHECKS
SYMPTOM RECOMMENDED CHECK
Low or no output:
Consistent Output Errors:
Fixed Output:
Erratic Output:
Check power supply for low dc output.
Check field wiring for shorts, opens, grounds or
excessive resistance.
Check that shutoff val ves are fully open.
Check for leaks in the connecting line or at
the transmitter connection.
Check for sediment or clogging in the connecting
line or at the transmitter connection.
Check for gas in liquid lines, or liquid in gas
lines.
Check zero and span adjustments using calibration
test setup.
Check that shutoff valves are fully open. Pressure
may be trapped in the connecting line.
Amplifier board may be defective.
Check loop wiring for shorts, opens, grounds or
intermittent connections.
Check piping for gas in liquid lines, or liquid in
gas lines.
Amplifier board may be defective.
1A.7 GP TRANSMITTER SPECIFICATIONS
Specifications that apply to the Series PX726A Transmitters are listed below. Those
specifications that are common to all PX726A transmitters are contained in Section 5
Specifications.
Maximum Input Ranges: 0-100 inH
details)
Overpressure Effect: +0.2% URL at maximum operating pressure
Wet End Materials: 316 SS
M-3601 GP Transmitters / 1A-9
O to 0-5000 psi (see Table 1A-C for
2
Process Connections: 1 in. NPT male
Mounting Position Effect
on Transmitter Accuracy: ±2.0 inH
O which can be corrected by calibration
2
TABLE 1A-C - TRANSMITTER INPUT RANGES
Model
Suffix (1)
(Code)
100WCGI
300WCGI
400WCGI
025GI
050GI
100GI
300GI
500GI
1KGI
3KGI
See Table 1A-A for Series PX726A Model Number Codes.
0%
Minumum
Range
0-17 inH
0-50 inH
0-67 inH
2
2
2
0-4 psi
0-8 psi
0-17 psi
0-50 psi
0-83 psi
0-167 psi
0-500 psi
O
O
O
100%
Maximum
Range
0-100 inH
0-300 inH
0-400 inH
0-25 psi
0-50 psi
0-100 psi
0-300 psi
0-500 psi
0-1000 psi
0-3000 psi
O
2
O
2
O
2
Maximum
Working
Pressure
300 inH
900 inH
1200 inH
75 psi
150 psi
300 psi
900 psi
1500 psi
3000 psi
4500 psi
Offered
For Series
PX725A
O
2
O
2
O
2
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
1A-10 / GP Transmitters M-3601
Section 2
INSTALLATION
2.1 INSTALLATION NOTES
Prior to installing the transmitter, factors such as environmental temperature, maintenance access, and transmitter construction materials will require consideration.
Environmental Temperature: The temperature operating ranges for the wet end and electronics assemblies of the transmitter are as follows:
1. Wet end w/ DC 200 fill: -40 to 220°F (-40 to 104°C)
2. Electronic - Amplifier Board -25 to 185°F (-32 to 85°C)
3. Electronic - Digital Indicator -22 to 158°F (-30 to 70°C)
When installing a transmitter, it is important to consider the temperature range of all
items listed above as each has different limits. For example, if item 1 were at the upper
limit of its range (220°F), item 2 would be 35°F over its limit of 185°F. Likewise, if the
same transmitter included a digital indicator, item 3, the indicator would be 62°F above its
158°F limit.
Under no circumstances should the internal temperature of the electronics housing be allowed to go above the upper limits specified above for items 2 and 3. Doing so will cause
output errors, and possibly result in damage to the electronic assemblies. Going below the
lower temperature limit can also lead to performance or failure problems. If temperature
extremes are anticipated, the transmitter should be installed in a more favorable environment or be provided with other means of protection.
Caution: The transmitter must always be operated within the temperature range of its wet
end and electronic assemblies. Prolonged operation under extreme conditions could result
in eventual transmitter damage.
Maintenance Access: Select a site that provides ease of access for maintenance and repairs.
Inspect the site for any potential hazards that could result in accidental damage to equipment or injury to persons. Clearly post any dangers that may not be apparent to operators.
Construction Materials : Prior to mounting the transmitter, check its construction materials
to insure that they are compatible with the process medium. Some gases or liquids will
react with certain metals and result in permanent damage to the transmitter. This type of
damage is not covered under the warranty agreement.
2.2 INSTALLATIONS IN HAZARDOUS AREAS
The information that follows only applies to transmitter models approved for use in
hazardous areas. Models without approval must never
M-3601 Installation / 2-1
be used for these installations.
The installation of equipment in hazardous areas must comply with the National Electrical
Code ANSI/NFPA-70, and ANSI/ISA S82.01, S82.02, & S82.03 standards. Transmitters
certified for use in hazardous areas will have the mark of the certifying agency inscribed on
the transmitter data plate.
The checklist that follows emphasizes some key points of safety with regard to installations
in hazardous areas.
1. All transmitter wiring that passes through hazardous areas must be enclosed in metal
conduit. The point where the conduit connection feeds into the transmitter’s housing
must be properly secured to prevent entry of gases or other ignitable substances into
the transmitter. Explosion-proof wiring practices must be followed to prevent flashback
through the conduit.
2. The cover of the transmitter must be screwed in hand tight and fully seated. The cover
must be replaced if it is damaged or shows stripped threads.
3. The cover of the unit must always be in place and secured when the transmitter is
powered. The cover must never be loosened or removed unless the atmosphere is made
safe or all electrical power is removed from the transmitter.
WARNING: Removing the cover of a transmitter while it is operating in a hazardous area
is dangerous and could result in fire or explosion.
WARNING: EXPLOSION HAZARD
Do Not disconnect equipment unless power has been disconnected and the area
is known to be nonhazardous.
Figure 2-1 - Dressing of Wire Leads
2.3 ELECTRICAL WIRING NOTES
All wiring connections cited in the text and illustrations must conform to the National
Electrical Code, and local authority. Only technically qualified persons should perform
wiring procedures.
2-2 / Installation M-3601
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