Gems Sensors 856 Training manual

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1.0 GENERAL INFORMATION
Every Model 856 has been tested and calibrated before shipment. Specific
performance specifications are listed on Page 7 of this Guide.
Gems Sensors 856 pressure transducers sense gauge pressure and convert this
pressure to a proportional high level analog output. Two output versions are
offered: A voltage output of .1 to 5.1 VDC, and a current output of 4 to 20 mA.
2.0 MECHANICAL INSTALLATION
2.1 Media Compatibility
Model 856 transducers are designed to be used with any gas or liquid compat-
ible with 17-4 PH Stainless Steel. (Hydrogen is not recommended for use with
17-4 PH SS.)
2.2 Environment
The operating temperature limits of the 856 are as follows:
Operating Temperature Range °F (C°)-40 to +260 (-40 to +125)
Compensated Temperature Range°F (C°)-4 to +176 (-20 to +80)
2.3 Pressure Fittings
Typically, standard pipe fittings and installation procedures should be used.
However, for very high pressure ranges in excess of 500 psig, we suggest the
use of a sealant such as Loctite Hydraulic Sealant. Excessive high torquing of
metal fittings may cause a slight shift of the output, but this shift can be
trimmed out by the zero adjustment. Torquing does not significantly affect
linearity or sensitivity.
2.4 Moisture Precautions
The Model 856 is provided with two 1/2”NPT female conduit ports for electrical
termination. These tapered pipe threads are tapped deeper than the NPT
standard,in accordance with industry guidelines. These ports must be sealed
according to standard industry practice, in order to prevent moisture ingress
into the Model 856.
2.5 Venting
The Model 856 is a true gauge pressure transducer. This means that the
reference side of the pressure sensing diaphragm must be vented to atmo-
sphere. If the reference side of the diaphragm were sealed (as in a sealed gauge
transducer), temperature changes would cause the reference pressure to vary.
This may affect the overall accuracy, especially in ranges lower than 500 psig.
The Model 856 provides a vent from the reference side of the sensor to the
inside of the housing and the conduit ports. The user-provided electrical
conduit must be vented to atmosphere in a clean dry location. (It is important
to prevent moisture ingress from the environment into the wiring chamber
or reference side of the transducer.)
Model 856
Gauge Pressure Transducer
Instruction Bulletin No.203527
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4.4 Current Output Span Adjustment
Span or full scale output adjustments should only be performed by using an
accurate pressure standard (electronic manometer, digital pressure gauge, etc.)
with at least comparable accuracy to the 856 transducer. With full range
pressure applied to the pressure port, the span may be adjusted by turning the
span potentiometer screw. The factory setting is 20mA (±.16mA).
5.0 MODEL 856 PERFORMANCE SPECIFICATIONS
For Ranges For Ranges
25 PSI and Higher Less Than 25 PSI
Accuracy RSS*(at constant temperature.) ±.13% FS ±0.25% FS
Non-Linearity, BFSL ±0.1% FS ±0.22% FS
Hysteresis 0.08% FS 0.10% FS
Non-Repeatability 0.02% FS 0.05% FS
*RSS of Non-Linearity, Non-Repeatability and Hysteresis.
Thermal Effects
Compensated Range °F(°C) -4 to +176 (-20 to +80) -4 to +176 (-20 to +80)
Zero Shift %FS/100°F (50°C) ±1.0 (±0.9) ±2.0 (±1.8)
Span Shift %FS/100°F (50°C) ±1.5 (±1.4) ±1.5 (±1.3)
Warm-up Shift ±0.1% FS total ±0.1% FS total
RETURN POLICY
Returns are accepted on stock items up to 30 days from date of order.
You must contact our Returns Department for a Return Authoriza-
tion (RA) number. Return the goods - freight prepaid - in the original
container and include original packing slip. C. O. D. returns are not
accepted. Gems reserves the right to apply restocking charges.
Tel: [phone]
Fax: [phone]
●Gems products must be maintained and installed
in strict accordance with the National Electrical
Code and the applicable Gems Product Instruction
Bulletin that covers installation,operating and
proper maintenance.Failure to observe this
information may result in serious injury or
damages.
●Please adhere to the pressure and temperature
limitations shown throughout this bulletin.These
limitations must not be exceeded. These pressures
and temperatures take into consideration possible
system surge pressures/temperatures and their
frequencies.
Important Points
●Selection of materials for compatibility with the
media is critical to the life and operation of Gems
products.Take care in the proper selection of
materials of construction, testing is required.
●Our sensors have been designed to resist shock and
vibration. However, shock and vibration should be
minimized.
●Our sensors must not be field-repaired.
●Physical damage sustained by product may render it
unserviceable.
SS2112 Rev.A 01/03
Gems Sensors
One Cowles Road
Plainville, CT 06062-1198
Toll-Free: 1-800-378-1600

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2.6 Mounting Accessories
The Model 856 is provided with a bracket
and two hex bolts for mounting and a 1/2”
NPT plug for the unused conduit opening.The
bracket is suitable for mounting with a U-bolt
or a band clamp.There are 1/4-20 UNC
threaded holes on the back of the 856
transducer for direct mounting and/or
grounding.
3.0 ELECTRICAL INSTALLATION
Wiring is through 1 1/2”conduit opening.
Remove the screw cover to access the remov-
able wiring terminal block connector. The
terminal block connector version has five
terminals for wiring +EXC, -EXC, ND, -OUT, and
+OUT (see Diagram 1).
Remove the terminal block connector to facilitate wiring to screw terminals. Refer to
the terminal block connector label fr terminal designations. (See Diagram 2 for screw
terminal designations.) After wiring,plug connector back into pin socket and neatly
tuck all wiring into wire recess cavity.
3.1 Voltage Output Units
The Model 856 is a 3-wire circuit.The -EXC and -OUT are commoned on the circuit.The
856 can operate from a 12 to 28 VDC excitation.The 856 has a 0.1 - 5.1 VDC output.
+Excitation; connect to 12-28 VDC power supply
+Output; connect to controller or monitor
-Output; connect to controller or monitor
-Excitation, connect to return or 12-28 VDC power supply
GND Connect to system or earth ground
Te Model 856 can be wired as a three wire device by connecting -output, excitation
and shield to a common ground. However, accuracy will be reduced with increase in
lead resistance.
Removable
Zero/Span
Access Plugs
Removable
Terminal Block
Connector
Screw Terminal
Designations
Voltage Connections
Current Connections
+ EXC
- EXC
GND
- Out
+ Out
Diagram 1
Diagram 2
+ EXC
- EXC
GND
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3.2 Current Output Units
The 4-20 mA current output units are designed to have current flow in one
direction only - PLEASE OBSERVE POLARITY.
We suggest that the electrical conduit shield be connected to the system’s loop
circuit ground to improve electrical noise rejection.
The Model 856 is a two-wire loop-powered 4 to 20mA current output unit and
delivers rated current into any external load of 0-800 ohms. (See Diagram 2 for
location of +EXC and -EXC current output screw terminals.) The current flows
into the + terminal and returns back to the power supply through the
- terminal. (The center GND terminal may be used for shielding.) The power
supply must be a DC voltage source with a voltage range between 9 and 30
measured between the + and - terminals. The unit is calibrated at the factory
with a 24 VDC loop supply voltage and a 250 ohm load.
Minimum Supply Voltage (VDC) = 9 + 0.02 x (resistance of receiver plus line).
Maximum Supply Voltage (VDC) = 30 + 0.004 x (resistance of receiver plus line).
4.0 CALIBRATION
The 856 transducer is factory calibrated and should require no field
adjustment. Whenever possible, any zero and/or span offsets should be
corrected by software adjustment in the user’s control system. However, both
zero and span adjustments are accessible by removing the screw top cover and
the adjustment access cover and turning the potentiometer screw inside. (See
Diagram 1 for the location of the Zero and Span potentiometers.)
4.1 Voltage Output Zero Adjustment
While monitoring the voltage between the positive output (+OUT) and
negative output (– OUT), and with the pressure port open to atmosphere,or
with zero pressure applied, the zero may be adjusted by turning the zero
potentiometer screw. The factory setting is 0.1 VDC (±25mV).
Note: –OUT and –EXC are commoned on the circuit.
4.2 Voltage Output Span Adjustment (Complete the zero adjust-
ment before setting span.)
Span or full scale output adjustments should only be performed by using an
accurate pressure standard (electronic manometer, digital pressure gauge, etc.),
with at least comparable accuracy to the 856 transducer. With full
range pressure applied to the pressure port, the span may be adjusted by
turning the span potentiometer screw. The factory setting is 5.1 VDC (±50mV).
4.3 Current Output Zero Adjustment
While monitoring the current output, and with the pressure port open to
atmosphere or with zero pressure applied, the zero may be adjusted by turning
the zero potentiometer screw. The factory setting is 4mA (±.08mA).