Product Bulletin 846 Transducers

846 Transducers			Tables Figures Print Version Collapse Expand

Type 846 Electro-Pneumatic Transducer

846 Transducers Description The 846 electro-pneumatic transducer (figure 1) is a rugged, field-mountable transducer that accepts an electrical input signal and converts it to a pneumatic output signal. Typically, the 4 to 20 mA is converted to 0.2 to 1.0 bar (3 to 15 psi). In the most common application, the transducer converts an electrical output signal from a controller to a pneumatic signal necessary to operate a control valve actuator or pneumatic positioner.
The transducer includes a patented deflector/nozzle design (figure 2) that consists of two nozzles positioned so that the constant air flow exiting the supply nozzle is directed at the entrance of the receiver nozzle. Each nozzle has a large bore of 0.41 mm (0.016 inches), which provides good resistance to plugging. The input current signal positions a deflector bar within the nozzle's flow stream. As the input signal changes, the deflector bar moves to alter the flow stream to the receiver nozzle, establishing a pilot pressure at the receiver nozzle. The pilot pressure, in turn, controls the booster stage and output of the transducer.
An electronic feedback control network constantly compares the value of the pneumatic output signal with the input current signal. A solid-state pressure sensor is part of the electronics package monitoring the pneumatic output (figure 4). A comparator circuit in the control network detects input-output deviations and adjusts the output by moving the deflector in the pilot stage to a corrected position. Because of this feedback network, the transducer can correct for error-producing effects such as variations in supply pressure and downstream leakage.

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Input Signal

4-20 mA DC, field adjustable split ranging.

Equivalent Circuit

See figure 5

Output Signal

Standard Performance: ■0.2 to 1.0 bar (3 to 15 psi). Rangeability between 0.1 to 1.2 bar (1 and 18 psi)
Multirange Performance: ■0 to 1.2 bar (0 to 18 psi), ■0.4 to 2.0 bar (6 to 30 psi), and ■0 to 2.3 bar (0 to 33 psi) nominal ranges. Actual rangeability available between 0.03 to 2.3 bar (0.5 and 33 psi)
Action: ■Direct (increasing input signal increases transducer output) (Minimum span,
6 psi) or ■Reverse (increasing input signal decreases transducer output) (Minimum span,
11 psi)

Supply Pressure

Standard Performance: 1.2 to 1.6 bar
(18 to 24 psi)
Multirange Performance:
Minimum: 0.2 bar (3 psi) [0.14 bar (2 psi) for a 2.3 bar (33 psi) output] greater than the maximum calibrated output pressure.
Maximum: 2.4 bar (35 psi)

Medium: Air or natural gas
Air Quality: Supply pressure must be clean, dry air that meets the requirements of ISA Standard 7.0.01. A maximum 40 micrometer particle size in the air system is acceptable. Further filtration down to 5 micrometer particle size is recommended. Lubricant content is not to exceed 1 ppm weight (w/w) or volume (v/v) basis. Condensation in the air supply should be minimized.
Natural Gas: Natural gas must be clean, dry, oil-free, and noncorrosive. H2S content should not exceed 20 ppm. Natural gas as the supply medium is only approved for CSA and FM approvals, as specified in tables 2 and 3. Type 846 is not recommended for use with aromatic gas.

Steady-State Air Consumption(1)

0.3 normal m3/hr (12 scfh) at 1.4 bar (20 psi) supply pressure.

Output Air Capacity(1)

Standard Performance: 6.4 normal m3/hr (240 scfh) at 1.4 bar (20 psi) supply pressure.
Multirange Performance: 9.7 normal m3/hr (360 scfh) at 2.5 bar (35 psi) supply pressure

Temperature Limits

Operating: -40 to 85°C (-40 to 185°F).
Storage: -40 to 93°C (-40 to 200°F).

Humidity Limits

0-100% condensing relative humidity.

Performance(2)

Linearity, Hysteresis, and Repeatability: ±0.3% of span.
Temperature Effect (total effect including zero and span): ±0.07%/°C (0.045%/°F) of span
Vibration Effect: ±0.3% of span per g during the following conditions:
5-15 Hz at 4 mm constant displacement
15-150 Hz at 2 g. 150-2000 Hz at 1 g.
per SAMA Standard PMC 31.1, Sec. 5.3, Condition 3, Steady State.
Shock Effect: ±0.5% of span, when tested per SAMA Standard PMC 31.1, Sec. 5.4.
Supply Pressure Effect: Negligible
Electromagnetic Interference (EMI): Tested per IEC 61326-1 (Edition 1.1). Meets emission levels for Class A equipment (industrial locations) and Class B equipment (domestic locations). Meets immunity requirements for industrial locations (Table A.1). Immunity performance is shown in table 1.
Leak Sensitivity: Less than 1.0% of span for up to 4.8 normal m3/hr (180 scfh) downstream leakage.
Overpressure Effect: Less than 0.25% of span for misapplication of up to 7.0 bar (100 psi) supply pressure for less than 5 minutes to the input port.
Reverse Polarity Protection: No damage occurs from reversal of normal supply current (4-20 mA) or from misapplication of up to 100 mA.

Connections

Supply and Output Pressure: 1/4-18 NPT internal connection.
Electrical: 1/2-14 NPT internal conduit connection.

Adjustments

Zero and Span: Screwdriver adjustments located in terminal compartment.

Remote Pressure Reading (optional)

ON or OFF; jumper selectable
Frequency Range: 5,000-8,000 Hz.
Amplitude: 0.4-1.0 Vp-p

Required Operating Voltage

Min. 6.0 V (at 4 mA)
Max. 7.2 V (at 20 mA)
with Remote Pressure Reading ON
Min. 6.4 V (at 4 mA)
Max. 8.2 V (at 20 mA)

Electrical Classification

Hazardous Area

Intrinsic Safety, Flameproof, and Div. 2

Intrinsic Safety, Flameproof and
Dust-Ignition Proof

Intrinsic Safety, Flameproof and Type n

Intrinsic Safety, Flameproof and Type n

Intrinsic Safety, Flameproof and Type n
Refer to tables 2, 3, 4, 5, and 6 for additional information.
Electrical Housing: NEMA 4X, CSA Enclosure Type 4X, IP66 per IEC60529, Tropicalization (Fungus test per MIL-STD-810)

Construction Materials

Housing: ■Low-copper aluminum with polyurethane paint, or ■ 316 stainless steel
O-Rings: Nitrile, except silicone for sensor O-rings.

Mounting

■Actuator, ■pipestand, or ■surface

Weight

Aluminum: 2.9 kg (6.5 lb) excluding options
Stainless Steel: 6.7 kg (14.8 lb) excluding options

Options

■67CFR filter regulator, ■supply and output gauges, ■remote pressure reading, or ■stainless steel mounting bracket

NOTE: Specialized instrument terms are defined in ANSI/ISA Standard 51.1 - Process Instrument Terminology
1. Normal m3/hr: normal cubic meters per hour (m3/hr, 0°C and 1.01325 bar, absolute). Scfm: standard cubic feet per minute (ft3/min, 60°F and 14.7 psig).
2. Performance values are obtained using a transducer with a 4 to 20 mA dc input signal, a 3 to 15 psig output, and 20 psig supply pressure.

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Vibration Resistant—The low-mass pilot stage, mechanically damped deflector bar, and rugged construction provide stable performance in vibration.
Large Diameter Nozzles—Large diameter nozzles, free-flow pilot stage design, and large internal pneumatic supply passages provide excellent tolerance to reducing the effects of contaminant buildup and erosion.
Increased Accuracy, Reduced Sensitivity to Supply Pressure Variations and Downstream Leakage—The electronic feedback control network monitors the pneumatic output signal, detects any input-output deviations and corrects them. This provides very high accuracy and allows the transducer to sense changes in the final element condition and rapidly optimize its air delivery.
Easy Maintenance—Major mechanical and electrical components are incorporated into a single field-replaceable ``master module" (figure 3). The transducer does not have to be removed from its mounting to facilitate troubleshooting or service. A separate field wiring compartment eases installation and maintenance.
Quick Diagnostic Checks and Remote Performance Monitoring—With Stroke Port, a constant bleed from the pilot stage vents through a hole in the module cover. Covering the hole increases the transducer output to confirm the proper operation of the pilot and booster stages and stroke the actuator. With optional Remote Pressure Reading, a frequency directly proportional to the output pressure is superimposed on the input signal wires.

Using a 275 HART® Communicator or frequency counter, an operator can monitor the Type 846 output pressure.

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Installation The transducer may be actuator, wall, panel, or pipestand mounted. Dimensions are shown in figures 7, 8, and 9.

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Ordering Information To determine what ordering information is required, refer to the specification table. Carefully review the description of each specification. Specify the desired choice whenever there is a selection available.
When ordering mounting parts, specify actuator, surface, or pipestand mounting. For actuator mounting, specify the actuator type, size, travel, and diaphragm pressure range. For all 657 and 667 actuators except size 80, specify whether actuator yoke or actuator casing mounting is desired (yoke mounting only is available on size 80 actuators).

Note
Neither Emerson, Emerson Process Management, nor any of their affiliated entities assumes responsibility for the selection, use, or maintenance of any product. Responsibility for the selection, use, and maintenance of any product remains with the purchaser and end-user.

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Table

Table 1. EMC Immunity Performance Criteria

Port	Phenomenon	Basic Standard	Test Level	Performance Criteria(1)
Enclosure	Electrostatic discharge (ESD)	IEC 61000-4-2	4 kV contact 8 kV air	A
	Radiated EM field	IEC 61000-4-3	80 to 1000 MHz @ 10V/m with 1 kHz AM at 80%	A
	Rated power frequency magnetic field	IEC 61000-4-8	60 A/m at 50 Hz	A
I/O signal/control	Burst (fast transients)	IEC 61000-4-4	1 kV	A
	Surge	IEC 61000-4-5	1 kV (line to ground only, each)	B
	Conducted RF	IEC 61000-4-6	150 kHz to 8 MHz at 3 Vrms	B
	Conducted RF	IEC 61000-4-6	8 kHz to 80 MHz at 3 Vrms	A
Specification limit = ±1% of span 1. A = No degradation during testing. B = Temporary degradation during testing, but is self-recovering.

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Table 2. Hazardous Area Classifications for Canada—CSA

Certification Body	Certification Obtained	Entity Rating	Temperature Code	Enclosure Rating
CSA	(Intrinsic Safety) Class/Division Intrinsic Safety Class I Division 1 Groups A,B,C,D per DWG 13B8779 Approved for use with natural gas	- - -	T4 (Tamb ≤40°C)	TYPE 4X
	(Explosion Proof) Class/Division Class I Division 1 Groups C,D Approved for use with natural gas	- - -	T4 (Tamb ≤ 80°C)	TYPE 4X
	Class I, Division 2, Groups A,B,C,D Class II, III Division 1, Groups E,F,G Approved for use with natural gas	- - -		TYPE 4X

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Table 3. Hazardous Area Classification for United Stated—FM

Certification Body	Certification Obtained	Entity Rating	Temperature Code	Enclosure Rating
FM	(Intrinsic Safety) Class/Division Class I, II, III Division 1 Groups A,B,C,D,E,F,G per drawing 13B8780 Approved for use with natural gas	Vmax = 40 VDC Imax = 185 mA Ci = 0.016 μF Li = 20 μH	T5 (Tamb ≤ 60°C)	NEMA 4X
	(Explosion Proof) Class/Division Class I, Division 1, Groups B,C,DApproved for use with natural gas - Groups C,D only	- - -	T5 (Tamb ≤ 60°C)	NEMA 4X
	Class I, Division 2, Groups A,B,C,D Class II, III Division 1, Groups E,F,G Not approved for use with natural gas	- - -	T5 (Tamb ≤ 60°C)	NEMA 4X

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Table 4. Hazardous Area Classifications—ATEX(1)

Certificate	Certification Obtained	Entity Rating	Temperature Code	Enclosure Rating
ATEX	II 1 G & D Gas EEx ia IIC T4,T5 —Intrinsic Safety Dust T 90°C (Tamb = 80°C)	Ui = 40 VDC Ii = 200 mA Pi = 1.0 W Ci = 8 nF Li = 20 μH	T4 (Tamb ≤ 80°C) T5 (Tamb ≤ 40°C)	IP66
	II 3 G & D Gas EEx nL IIC T5,T6 —Type n Dust T 95°C (Tamb = 85°C)	- - -	T5 (Tamb ≤ 85°C) T6 (Tamb ≤ 74°C)	IP66
	II 2 G & D Gas EEx d IIB T5/T6 —Flameproof Dust T 90°C (Tamb = 80°C)	- - -	T5 (Tamb ≤ 80°C) T6 (Tamb ≤ 65°C)	IP66
1. Not approved for use with natural gas as the supply medium.

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Table 5. Hazardous Area Classifications—IECEx(1)

Certificate	Certification Obtained	Entity Rating	Temperature Code	Enclosure Rating
IECEx	Gas Ex ia IIC T4/T5 —Intrinsic Safety Dust DIP A20 TA 90°C IP66	Ui = 40 VDC Ii = 200 mA Pi = 1.0 W Ci = 8 nF Li = 20 μH	T4 (Tamb ≤ 80°C) T5 (Tamb ≤ 40°C)	IP66
	Gas Ex nL IIC T5/T6 —Type n Dust DIP A22 TA 90°C IP66	- - -	T5 (Tamb ≤ 80°C) T6 (Tamb ≤ 75°C)	IP66
	Dust DIP A20 TA 90°C IP66	- - -	- - -	IP66
	Gas Ex d IIB T5/T6 —Flameproof DustDIP A21 TA 90°C IP66	- - -	T5 (Tamb ≤ 80°C) T6 (Tamb ≤ 65°C)	IP66
1. Not approved for use with natural gas as the supply medium.

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Table 6. Hazardous Area Classifications—GOST(1)

Certificate	Certification Obtained	Entity Rating	Temperature Code	Enclosure Rating
GOST	Gas Ex ia IIC T4/T5 —Intrinsic Safety	Ui =30 V Ii = 200 mA Pi = 1.2 W Ci = 10 nF Li = 20 μH	T4 (Tamb ≤ 80°C) T5 (Tamb ≤ 40°C)	IP66
	Gas Ex d IIB T5/T6 —Flameproof	- - -	T5 (Tamb ≤ 80°C) T6 (Tamb ≤ 65°C)	IP66
	Gas Ex nL IIC T5/T6—Type n	- - -	T5 (Tamb ≤ 80°C) T6 (Tamb ≤ 74°C)	IP66
1. Not approved for use with natural gas as the supply medium.

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62.1:846
August 2007
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