Fisher 846 User manual

D102077X012
EFisher Controls International, Inc. 1994, 1995; All Rights Reserved
Fisher, Fisher-Rosemount, and Managing The Process Better are marks owned by Fisher
Controls International, Inc. or Fisher-Rosemount Systems, Inc.
HART is a mark owned by Rosemount Inc.
All other marks are the property of their respective owners.
This product may be covered by one or more of the following patents (4,481,967; 4,534,376;
4,638,830; 4,653,523; 4,665,938; 4,760,859; 4,777,826; 4,901,756) or under pending patent
applications.
Fisher-Rosemount satisfies all obligations coming from legislation
to harmonise product requirements in the European Union.
Type 846 Electro-Pneumatic Transducer
Contents
1. Introduction
Scope of Manual 1–1. . . . . . . . . . . . . . . . . . . . . . . . . .
Description 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Installation
Mounting 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Connections 2–1. . . . . . . . . . . . . . . . . . . . .
Supply Pressure 2–1. . . . . . . . . . . . . . . . . . . . . . . . .
Output Pressure 2–3. . . . . . . . . . . . . . . . . . . . . . . . .
Electrical Connections 2–5. . . . . . . . . . . . . . . . . . . . .
Stroke Port 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exhaust Port 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Signal Interruption 2–6. . . . . . . . . . . . . . . . . . . . . . . . .
3. Calibration
Standard Performance:
Full Range Input, Direct Action 3–1. . . . . . . . . . .
Multirange Performance:
Full Range Input, Direct Action 3–2. . . . . . . . . . .
Standard Performance:
Split Range Input, Direct Action 3–2. . . . . . . . . . .
4 to 12 mA Input Signal 3–2. . . . . . . . . . . . . . . . . . .
12 to 20 mA Input Signal 3–2. . . . . . . . . . . . . . . . . .
Standard Performance:
Full Range Input, Reverse Action 3–3. . . . . . . . .
Multirange Performance:
Full Range Input, Reverse Action 3–3. . . . . . . . .
Standard Performance:
Split Range Input, Reverse Action 3–3. . . . . . . .
4 to 12 mA Input Signal 3–3. . . . . . . . . . . . . . . . . . .
12 to 20 mA Input Signal 3–3. . . . . . . . . . . . . . . . . .
Transporting the Module Final Assembly 3–4. . . . .
4. Principle of Operation
Electronic Circuit 4–1. . . . . . . . . . . . . . . . . . . . . . . . . .
Magnetic Actuator 4–1. . . . . . . . . . . . . . . . . . . . . . . . .
Pilot Stage 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Booster Stage 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. Troubleshooting
Diagnostic Features 5–1. . . . . . . . . . . . . . . . . . . . . . .
Stroke Port 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Remote Pressure Reading (RPR) 5–1. . . . . . . . . .
Using the HART Communicator to
Read the RPR Signal 5–1. . . . . . . . . . . . . . . . .
Using a Frequency Counter to
Read the RPR Signal 5–1. . . . . . . . . . . . . . . . .
In-service Troubleshooting 5–2. . . . . . . . . . . . . . . . .
Troubleshooting in the Shop 5–4. . . . . . . . . . . . . . . .
6. Maintenance
Module Final Assembly 6–1. . . . . . . . . . . . . . . . . . . .
Removing the Module Final Assembly 6–1. . . . . .
Replacing the Module Final Assembly 6–3. . . . . .
Electronic Circuit Board 6–4. . . . . . . . . . . . . . . . . . . .
Optional Remote Pressure Reading (RPR)
Jumper 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Range Jumper 6–5. . . . . . . . . . . . . . . . . . . . . . . . . .
Action 6–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removing the Electronic Circuit Board 6–5. . . . . .
Replacing the Electronic Circuit Board 6–5. . . . . .
Pilot/Actuator Assembly 6–6. . . . . . . . . . . . . . . . . . . .
Action 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removing the Pilot/Actuator Assembly 6–6. . . . . .
Replacing the Pilot/Actuator Assembly 6–6. . . . . .
Module Subassembly 6–7. . . . . . . . . . . . . . . . . . . . . .
Terminal Compartment 6–7. . . . . . . . . . . . . . . . . . . . .
Exhaust and Stroke Port Screens 6–7. . . . . . . . . . .
7. Parts List
8. Loop Schematics
Section 1
Introduction
Scope of Manual
This instruction manual provides installation, operat-
ing, calibration, maintenance, and parts ordering in-
formation for the Type 846 electro-pneumatic trans-
ducer. Refer to separate manuals for instructions
covering equipment used with the transducer.
Instruction Manual
Form 5354
November 1995Type 846

Type 846
1–2
Figure1-1. Type846 Electro-Pneumatic TransducerMounted
on a Type667 Actuator
W6307–1/IL
Only personnel qualified through training or experience
should install, operate, or maintain the transducer. If
there are any questions concerning the instructions in
this manual, contact your Fisher sales office or sales
representative before proceeding.
Description
The Type 846 electro-pneumatic transducer, shown in
figure 1-1, accepts an electrical input signal and pro-
duces a proportional pneumatic output. Typically, 4 to
20 mA is converted to 3 to 15 psi (0.2 to 1.0 bar).
Models are available in direct or reverse action and
field-selectable full or split range inputs. See Section 3
Calibration for more information on input/output com-
binations.
The most common application of the Type 846 is to
receive an electrical signal from a controller and pro-
duce a pneumatic output for operating a control valve
actuator or positioner. The Type 846 may also be used
to transduce a signal for a pneumatic receiving instru-
ment.
The Type 846 is an electronic I/P transducer. It has a
single electronic circuit board, as shown in Figure 1-2.
Figure1-2. Type846Modular Construction
A6643/IL
MODULE COVER
MODULE FINAL
ASSEMBLY
ELECTRONIC
CIRCUIT BOARD
MODULE HOUSING
TERMINAL BLOCK
TERMINAL
COMPARTMENT
COVER
The circuit contains a solid-state pressure sensor that
monitors output pressure and is part of an electronic
feedback network. The self-correcting ability provided
by the sensor/circuit combination allows the Type 846
to produce a very stable and responsive output signal.
All active mechanical and electrical components of the
Type 846 are incorporated into a single, field-replace-
able module called the module final assembly, shown
in Figure 1-2. The module final assembly contains the
electronic circuit board, pilot/actuator assembly, and
booster stage. The module final assembly is easily
removed by unscrewing the module cover. Its design
minimizes parts and reduces the time required for re-
pair and troubleshooting.
The terminal compartment and module compartment
are separated by a sealed compartment wall. This
multi-compartment housing also protects the electron-
ics from contaminants and moisture in the supply air.
Specifications
Specifications for the Type 846 transducer are listed in
table 1-1.

Type 846
1–3
Table1-1. Specifications
Input Signal(1)
J4 to 20 mA dc, J4 to 12 mA dc, or J12 to 20
mA dc. Field adjustable split ranging
Output Signal(1)
Standard Performance: J3 to 15 psig (0.2 to 1.0
bar). Rangeability between 1 and 18 psi (0.1 to 1.2
bar).
Multirange Performance: J0.5 to 18 psig (0,03 to
1.2 bar), J6 to 30 psig (0.4 to 2.0 bar), and J0.5
to 33 psig (0.03 to 2.3 bar). Rangeability between
0.5 and 33 psi (0.03 to 2.3 bar).
Action: JDirect (increasing input signal increases
transducer output) (Minimum span, 6 psi) or JRe-
verse (increasing input signal decreases transducer
output) (Minimum span, 11 psi)
Supply Pressure(1)
Standard Performance
18 to 24 psig ( 1.2 to 1.6 bar)
Multirange Performance
Minimum: 3 psig(4) (0.2 bar) greater than the maxi-
mum calibrated output pressure
Maximum: 35 psig (2.4 bar)
Steady-State Air Consumption(2)
0.20 scfm (0.3 normal m3/hr) at 20 psig (1.4 bar)
supply pressure
Output Air Capacity(2)
Standard Performance: 4.0 scfm (6.7 normal
m3/hr) at 20 psig (1.4 bar) supply pressure
Multirange Performance: 6.0 scfm (9.0 normal
m3/hr) at 35 psig (2.5 bar) supply pressure
Temperature Limits
Operating:(1) –40 to 185°F (–40 to 85°C).
Storage:(1) –40 to 200°F (–40 to 93°C).
Humidity Limits
0 to 100% condensing relative humidity.
Performance(3)
Linearity(1), Hysteresis(1), and Repeatablility:
"0.3% of span. Reference SAMA PMC 31.1.
Temperature Effect (total effect including zero
and span): "0.045%/°F (0.07%/°C) of span
Vibration Effect: "0.3% of span per g during the
following conditions:
5 to 15 Hz at 4 mm constant displacement
15 to 150 Hz at 2 g. 150 to 2000 Hz at 1 g.
per SAMA Standard PMC 31.1-1980, 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):(1) When
tested per SAMA Standard PMC 33.1C–1978,
change in steady–state deviation is less than
"0.1% of span at 30 V/m, Class 3 (wire in conduit),
ABC.
"1.0% of span at 10 V/m, Class 2 (wire not in con-
duit), ABC.
Leak Sensitivity:(2) Less than 1.0% of span for up
to 3.0 scfm (5.0 normal m3/hr) downstream leak-
age.
Overpressure Effect: Less than 0.25% of span for
misapplication of up to 100 psi (7.0 bar) supply
pressure for less than 5 minutes to the input port.
Reverse Polarity Protection: No damage occurs
from reversal of normal supply current (4 to 20 mA)
or from misapplication of up to 100 mA.
Connections
Supply and Output Pressure: 1/4–18 NPT female
connection.
Electrical: 1/2–14 NPT female conduit connection
Adjustments
Zero and Span: screwdriver adjustments located in
terminal compartment.
Remote Pressure Reading (optional)
Jumper selectable, ON or OFF, if unit includes op-
tion
Frequency Range: 5,000 to 8,000 Hz.
Amplitude: 0.4 to 1.0 Vp-p
Required Operating Voltage
with Remote pressure Reading Off
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)
Weight
6.5 lb (2.9 kg) excluding options
Hazardous Locations Certifications
Refer to the Hazardous Area Classification Bulletin
9.2:001 and the transducer nameplate (see figure
1-3).
–Continued–

Type 846
1–4
Table1-1. Specifications (continued)
Housing Classification
CSA Type 4X, NEMA 4X, designed to meet IP66,
tropicalization (Fungus test per MIL-STD-810)
Options
JType 67AFR filter regulator, Jsupply and output
gauges or Jtire valves, Jremote pressure read-
ing, Jmodule cover with multiple stroke ports,
Jstainless steel housing, or Jstainless steel
mounting bracket
1. This term is defined in ISA Standard S51.1-1979.
2. Scfm—Standard cubic feet perminute (60_Fand14.7 psia). Normalm3/hr—Normal cu-
bic meters per hour (0_C and 1.01325 bar, absolute).
3. Performance values are obtained usinga transducerwith a4.0 to20 mAdcinput signal,
a 3 to 15 psig (0.2 to 1.0 bar) output, and a 20 psig (1.4 bar) supply pressure.
4. 2 psig (0.14 bar) for a 33 psig (2.3 bar) output
Figure1-3. TypicalNameplate
INFORMATION IN THIS AREA
IDENTIFIES THE HAZARDOUS AREA
CLASSIFICATION AND APPROVALS
FOR THE PRODUCT SPECIFIED ON
THE EQUIPMENT ORDER
B2464

Type 846
2–1
Section2 Installation
When a control valve is ordered with a Type 846 trans-
ducer specified to be mounted on the actuator, the
factory-mounted transducer is connected to the actua-
tor with the necessary tubing and calibrated to the
specifications on the order.
If the transducer is purchased separately for mounting
on a control valve already in service, all the necessary
mounting parts are furnished, if ordered. This includes
the appropriate bracket for attaching the unit to an ac-
tuator boss (with tapped holes) or for attaching it to the
diaphragm casing.
If preferred, mounting parts can be supplied for mount-
ing the transducer on a 2-inch (51 mm) diameter pi-
pestand, a flat surface, or a bulkhead.
Mounting
Figures 2-1, 2-2, and 2-NO TAG show the mounting
dimensions. Mount the unit with the stroke port down.
This allows any moisture buildup in the terminal
compartment to drain to the signal wire conduit en-
trance. Any moisture in the pilot stage area will be ex-
pelled through the stroke port without affecting pilot
stage operation. As an alternative, the Type 846 may
be mounted horizontally. However, it must be mounted
so that the flat bracket-mounting surface is down. In
applications with excessive moisture in the supply air,
vertical mounting allows the most effective drainage
through the stroke port.
Before mounting the Type 846, note the following rec-
ommendations:
DEnsurethatall bolts arefullytightened. The recom-
mended torque is 16 lbfSft (22 NSm).
DBolts that connect to the Type 846 and to a valve
actuator should have thelock washer placeddirectly be-
neath the bolt head and the flat washer placed between
the lock washer and bracket. All other boltsshould have
the lock washer next to the nut, and the flat washer
placed between the lock washer and bracket.
DDo not mount the Type 846 in a location where for-
eign material may cover the stroke port or exhaust port.
See the descriptions of the stroke port and exhaust port
later in this section.
Pressure Connections
As shown in figure 2-1, all pressure connections are
1/4-18 NPT female connections. Use 3/8-inch (9.5
mm) outside diameter tubing for the supply and output
connections.
Supply Pressure
WARNING
Personal injury or property damage may
occur from an uncontrolled process if
the supply medium is not clean, dry, oil-
free, or non-corrosive gas. Industry
instrument air quality standards de-
scribe acceptable dirt, oil, and moisture
content. Due to the variability in nature
of the problems these influences can
have on pneumatic equipment, Fisher
Controls has no technical basis to rec-
ommend the level of filtration equipment
required to prevent performance degra-
dation of pneumatic equipment. A filter
or filter regulator capable of removing
particles 40 microns in diameter should
suffice for most applications. Use of
suitable filtration equipment and the es-
tablishment of a maintenance cycle to
monitor its operations is recommended.
WARNING
Explosions may cause death or serious
injury. Do not operate the Type 846 with
the CENELEC flameproof options at a
supply pressure in excess of 20 psi (1.4
bar). Doing so invalidates the CENELEC
flameproof certifications and could al-
low flames to spread from the unit po-
tentially igniting and causing an explo-
sion.
The supply medium must be clean, dry air or noncor-
rosive gas that meets the requirements of ISA Stan-
dard S7.3-1975 (R1981). An output span of 3 to 15
psig (0.2 to 1.0 bar) requires a nominal supply pres-
sure of 20 psig (1.4 bar) and a flow capacity not less
than 4 SCFM (0.11 m3/min). For multirange perfor-
mance units with higher output spans, the supply pres-
sure should be at least 3 psig (0.2 bar) greater than
the maximum calibrated output pressure, but should
not exceed 35 psig (2.4 bar).
The air supply line can be connected to the 1/4–18
NPT supply port, or to the supply port of a filter-regula-
tor mounted directly to the transducer.
The mounting boss for the air supply connection con-
tains two 5/16–18 UNC tapped holes that are 2-1/4
inches apart. The tapped holes allow direct connection
of a filter-regulator having a matching through-bolt pat-
tern. A filter-regulator with mounting hardware is avail-
able. The mounting hardware consists of two 5/16–18
x 3-1/2 inch grade 5 bolts and one O-ring. See Table
6-1 for the O-ring size. The O-ring is positioned in the

Type 846
2–2
Figure2-1. Type846Dimensionsand Connection Locations
4.64
(118)
4.62
(117)
STROKE PORT
OUTPUT GAUGE PORT
1/4-18 NPT
NAMEPLATE EXHAUST PORT
UNDERNEATH NAMEPLATE
CONDUIT CONNECTION
1/2 - 14 NPT
OUTPUT PORT
1/4 - 18 NPT


WIRING CONNECTION
1.38
(35)
1.16
(29)
1.13
(29)
2.31
(59) COVER
REMOVAL
4.33
(110)
4.00
(102)
5/16-18 (2)
O-RING GROOVE
FOR FILTER
REGULATOR
SUPPLY PORT
1/4-18 NPT
POSITIVE
NEGATIVE
GROUND
NOTE;
DIMENSIONS ARE IN INCHES (MILLIMETERS).
B2473/IL
TEST PINS

Type 846
2–3
FOR PROPER MOISTURE
DRAINAGE THIS END
MUST BE UP
Figure2-2. Typical Type 846 Dimensions with Type 67AFRFilter/Regulator andGauges
2.62
66.5 COVER REMOVAL CLEARANCE
8.81
223.8
2.75
69.9
3.06
77.7
5.38
136.7
2.25
57.1
2.00
50.8
.34
8.6
MODULE COVER
REMOVAL CLEARANCE
6.38
162.1
.25
6.4
8.44
214.4 MAX
YOKE MOUNTED
NOTE:
THE MOUNTING POSITIONS SHOWN ALLOW ANY MOISUTRE BUILUP IN THE TERMINAL COMPARTMENT
TO DRAIN TO THE SIGNAL WIRE CONDUIT ENTRANCE. DO NOT MOUNT THE TRANSDUCER WITH THE TERMINAL
COMPARTMENT COVER ON THE BOTTOM; MOISTURE MAY ACCUMULATE IN THE TERMINAL COMPARTMENT
OR PILOT STAGE, PREVENTING PROPER TRANSDUCER OPERATION. THE VERTICAL MOUNT IS MOST EFFECTIVE
FOR MOISTURE DRAINAGE IN WET APPLICATIONS.
1
14B7361
A6626–1/IL
O-ring gland of the filter-regulator mounting boss. The
filter-regulator contains a 1/4 NPT output port for a
supply gauge. A threaded plug must be installed in the
gauge port when a gauge is not used.
Output Pressure
Connect the output signal line to the Type 846 at the
output port. The output port is 1/4–18 NPT, as shown
in Figure 2-1. The output gauge port can be used as
an alternate signal port. If the gauge port is used as a
signal port, a threaded plug must be installed in the
output port.
The output gauge port allows connection of an output
gauge to provide local output signal indication. The
output gauge port is 1/4–18 NPT. If an output gauge is
not specified, a threaded plug is shipped with the Type
846. The plug must be installed in the output gauge
port when the port is not used.
WARNING
The following conditions may cause fail-
ure of the output gauge resulting in per-
sonal injury, and damage to the trans-
ducer and other equipment:
pressure beyond the top of the
gauge scale.
excessive vibration.
pressure pulsation.
excessive instrument temperature.
corrosion of the pressure contain-
ing parts.
other misuse.
Refer to ANSI B40.1-1980. Do not use on
oxygen service.

Type 846
2–4
Figure2-2. Typical Type 846 Dimensions With Type 67AFRFilter/Regulator andGauges(continued)
2.62
66.5 COVER REMOVAL CLEARANCE
3.06
77.7
MODULE COVER
REMOVAL CLEARANCE
FOR PROPER MOISTURE
DRAINAGE THIS END
MUST BE UP
NOTES:
THE MOUNTING POSITIONS SHOWN ALLOW ANY MOISUTRE BUILUP IN THE TERMINAL COMPARTMENT
TO DRAIN TO THE SIGNAL WIRE CONDUIT ENTRANCE. DO NOT MOUNT THE TRANSDUCER WITH THE TERMINAL
COMPARTMENT COVER ON THE BOTTOM; MOISTURE MAY ACCUMULATE IN THE TERMINAL COMPARTMENT
OR PILOT STAGE, PREVENTING PROPER TRANSDUCER OPERATION. THE VERTICAL MOUNT IS MOST EFFECTIVE
FOR MOISTURE DRAINAGE IN WET APPLICATIONS.
IF MOUNTED ON HORIZONTAL PIPE, THE I/P MUST BE ON TOP OF THE PIPE FOR PROPER MOISTURE DRAINAGE.
1
14B7363
A6627–1/IL
10.25
260.4 MAX
5.38
136.7
6.38
162.1
PIPE STAND MOUNTED
8.81
223.8
2.00
50.8
2.38
60.5∅
6.19
157.2
TYPE 67AFR
1/4-18 NPT
SUPPLY CONN
FOR PROPER MOISTURE
DRAINAGE THIS END
MUST BE UP
9.7/.38∅
MOUNTING HOLE
4 PLACES
9.69
246.1 MAX
6.38
162.1
2.62
66.5 COVER REMOVAL CLEARANCE
8.31
211.1
2.38
60.5
3.50
88.9
.75
19.0
3.50
88.9
5.38
136.7 MODULE COVER
REMOVAL CLEARANCE
2
14B7332
A6625–1/IL

Type 846
2–5
Figure2–3. Dimensions for Type 846with CENELECCertifications
TERMINAl
COMPARTMENT
COVER
COVER LOCK
INTERNAL
HEX DRIVE
ROUND HEAD
SCREW (3 mm)
4.75
(121) MODULE COVER
HOUSING
EXTERNAL EARTHING CONNECTION, SST TERMINAL
CLAMP AND SLOTTED M5 SCREW AND SPLIT
RING WASHER
3.62
(92)
6.38
(162)
4.75
(121)
INCH
(mm)
B2465/IL
Electrical Connections
WARNING
Explosions may result in death or seri-
ous injury. In explosive atmospheres,
remove power and shut off the air sup-
ply to the I/P unit before attempting to
remove the terminal compartment cover
or module cover. Failure to do so could
result in electrical spark or explosion.
CAUTION
Excessive current can damage the
transducer. Do not connect the Type
846 to an input current of more than 100
mA.
Signal wiring is brought to the terminal compartment
through a 1/2–14 NPT housing conduit connection,
shown in Figure 2-1. Where condensate is common,
use a conduit drip leg to help reduce liquid buildup in
the terminal compartment and avoid shorting of the
input signal. Electrical connections are made at the
terminal block. An internal grounding lug is provided to
facilitate a separate ground when required. As shown
in figure 2-NO TAG, units with CENELEC certification
also have an external earthing connection. The use of
shielded cable will ensure proper operation in electri-
cally noisy environments.
Connect the positive signal lead to the positive termi-
nal, marked +. Connect the negative signal lead to the
negative terminal, marked –.
Note
Units with the Remote Pressure Reading
(RPR) option may cause interference
with the analog output signal from some
instrumentation systems. This problem
may be solved by placing a 0.2 microfa-
rad capacitor or a HART filter across the
output terminals.

Type 846
2–6
WARNING
Unscrewing the module cover removes
power from the electronics and the out-
put signal will be 0.0 psig. An uncon-
trolled process may result in death or
serious injury. Before removing the
module cover, ensure the device is
properly controlled.
Stroke Port
WARNING
Personal injury and property damage
could result from fire or explosion of ac-
cumulated gas. During normal opera-
tion, supply air is vented to the atmo-
sphere through the stroke port and
exhaust port. If a flammable gas is used
as the supply air, the area into which it
is vented must be classified as a Divi-
sion I hazardous area.
The constant bleed of supply air from the pilot stage is
directed out the stroke port, which is a screened hole
located at the center of the module cover. Figure 2-1
shows the location of the stroke port. Before installing
the Type 846, ensure the stroke port is clear. Do not
mount the Type 846 in a location where foreign materi-
al may cover the stroke port. For information on using
the stroke port, refer to Section 5 – Troubleshooting.
Exhaust Port
The Type 846 exhausts through a screened port lo-
cated beneath the instrument nameplate. Figure 2-1
shows the location of the exhaust port. The nameplate
holds the screen in place. Exhaust will occur with a
reduction in output pressure. The Type 846 should not
be mounted in a location where foreign material may
clog the exhaust port.
Signal Interruption
Upon loss of input current, or if input current de-
creases below 3.3 $0.3 mA, the output of the direct
action unit will decrease to less than 1 psig (0.1 bar).
In the same situation, the output of the reverse action
unit will increase to near supply pressure.

Type 846
3–1
Figure3-1. Connecting a Current or Voltage
SourceforCalibration




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
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Section3 Calibration
Calibration of the Type 846 requires either an accurate
current generator or an accurate voltage generator
with a precision 250-ohm, 1/2-watt resistor. Figure 3-1
shows how to connect either device.
Calibration also requires a precision output indicator
and a minimum nonsurging air supply of 3 SCFM (5.0
Normal m3/hr) at 20 psig (1.4 bar) for standard perfor-
mance units. For multirange performance units, the air
supply must be at least 3 psi (0.2 bar) greater than the
maximum calibrated output pressure, up to 35 psig
(2.4 bar) maximum.
For ease of calibration, the output load volume, includ-
ing the output tubing and output indicator, should be a
minimum of 2 cubic inches (33 cm3). Review the infor-
mation under Signal Interruption in Section 2 before
beginning the calibration procedure.
Before calibration, determine the type of input (full or
split range), and the type of output action (direct or
reverse). Consult the factory for split range output cal-
ibration. Also, determine if the unit offers standard or
multirange performance. The Type 846 supports eight
basic input/output combinations:
Standard Performance
DFull Range Input, Direct Action
DSplit Range Input, Direct Action
DFull Range Input, Reverse Action
DSplit Range Input, Reverse Action
Multirange Performance
DFull Range Input, Direct Action
DSplit Range Input, Direct Action(1)
DFull Range Input, Reverse Action
DSplit Range Input, Reverse Action(1)
The input range is selected by changing the position of
a jumper located on the electronic circuit board. Refer
to Electronic Circuit Board in Section 6, and Figure
6-5 for the location and instruction on placement.
CAUTION
Excessive current can damage the
transducer. Do not connect the Type 846
to an input current of more than 100 mA.
Standard Performance: Full Range Input,
Direct Action
Use the following procedure to achieve a standard 3 to
15 psi (0.2 to 1.0 bar) output span for a 4 to 20 mA
input signal:
1. Remove the module final assembly from the hous-
ing. Refer to Removing the Module Final Assembly
in Section 6 for an explanation of how to disengage
the module final assembly.
2. Confirm that the unit is direct acting. A green elec-
tronic circuit board identifies direct-acting units. Refer
to Action under the heading Electronic Circuit
Board in Section 6 for more information on direct act-
ing units.
3. Position the range jumper in the H position for High
Range. Figure 6-5 shows the circuit board jumper
positions.
4. Replace the module final assembly in the housing.
Refer to Replacing the Module Final Assembly in
Section 6 for an explanation of how to engage the
module final assembly.
5. Connect the air supply to the air supply port.
6. Connect a precision output indicator to the output
signal port.
7. Make sure that the output gauge port has an output
gauge or a threaded plug installed. A threaded plug is
provided for units shipped without output gauges.
8. Remove the terminal compartment cover.
9. Connect the current source (or voltage source)
positive lead (+) to the terminal block positive (+) and

Type 846
3–2
the current source (250-ohm resistor lead) negative
lead (–) to the terminal block negative (–). Refer to
Figure 3-1.
CAUTION
Excessive current can damage the
transducer. Do not connect the Type 846
to an input current of more than 100 mA.
10. Apply a 4.0 mA (Vm= 1.0 V) signal, and adjust
the zero screw to achieve a 3.0 psig (0.2 bar) output.
The output increases with clockwise rotation of the
zero screw.
11. Apply a 20.0 mA (Vm= 5.0 V) signal, and adjust
the span screw to achieve a 15.0 psig (1.0 bar) output.
The output increases with clockwise rotation of the
span screw.
12. Repeat Steps 10 and 11 to verify and complete
the calibration.
Multirange Performance: Full Range
Input,(2) Direct Action
Use the following procedure with a multirange perfor-
mance unit to achieve the desired direct action output
span for a 4 to 20 mA input signal:
1. Perform steps 1 through 9 of the calibration proce-
dure for Standard Performance: Full Range Input,
Direct Action.
2. Apply a 4.0 mA (Vm= 1.0 V) signal, and adjust the
zero screw to achieve the desired lower psi limit of the
output range. The lower limit must be between 0.5
psig (0.03 bar) and 9.0 (0.6 bar). The output increases
with clockwise rotation of the zero screw.
3. Apply a 20.0 mA (Vm= 5.0 V) signal, and adjust
the span screw to achieve the desired upper psi limit
of the output range. The span must be at least 6.0 psi
(0.4 bar). The maximum upper limit is 30.0 psig (2.0
bar). The output increases with clockwise rotation of
the span screw.
4. Repeat steps 2 and 3 to verify and complete the
calibration.
Standard Performance: Split Range
Input, Direct Action
4 to 12 mA Input Signal
Use the following calibration procedure to produce a 3
to 15 psi (0.2 to 1.0 bar) output span for a 4 to 12 mA
input signal:
1. Perform steps 1 through 9 of the calibration proce-
dure for Standard Performance: Full Range Input,
Direct Action.
2. Apply an input of 4.0 mA (Vm= 1.0 V), and adjust
the zero screw to achieve an output of 3.0 psig (0.2
bar).
3. Apply an input of 12.0 mA (Vm= 3.0 V), and adjust
the span screw to achieve an output of 15.0 psig (1.0
bar).
4. Repeat steps 2 and 3 to verify and complete the
calibration.
12 to 20 mA Input Signal
Use the following calibration procedure to produce a 3
to 15 psi (0.2 to 1.0 bar) output span for a 12 to 20 mA
input signal:
Note
There may be some span interaction
with zero in this range, and the follow-
ing steps compensate for this.
1. Perform steps 1 through 9 of the calibration proce-
dure for Standard Performance: Full Range Input,
Direct Action.
2. Apply an input of 4.0 mA (Vm= 1.0 V), and adjust
the zero screw to achieve an output of 3.0 psig (0.2
bar).
3. Apply an input of 12.0 mA (Vm= 3.0 V), and adjust
the span screw to achieve an output of 15.0 psig (1.0
bar).
4. Maintain the input of 12.0 mA (Vm= 3.0 V), and
adjust the zero screw to achieve an output of 3.0 psig
(0.2 bar). The unit may not turn down this low; if it
does not, go to step 7.
5. If the output reaches 3.0 psig (0.2 bar) in step 4,
apply an input of 20.0 ma (Vm= 5.0 V) and note the
error (the actual reading versus 15.0 psig). Adjust the
span screw to overcorrect the error by a factor of two.
For example, if the reading was 14.95 psig (0.9 bar),
adjust the span screw to achieve an output of 15.05
psig (1.1 bar).
6. Repeat steps 4 and 5 to verify and complete the
calibration.
7. Turn off the air supply. Remove the module final
assembly from the housing. Please the range jumper
in the L position for Low Range, as indicated in Figure
6-5. Replace the module final assembly. Turn on the
air supply.
8. Apply an input of 12.0 mA (Vm= 3.0 V), and adjust
the zero screw to achieve an output of 3.0 psig (0.2
bar).
9. Apply an input of 20.0 mA (Vm= 5.0 V), and note
the error (the actual reading versus 15.0 psig). Adjust

Type 846
3–3
the span screw to overcorrect the error by a factor of
two. For example, if the reading was 14.95 psig (0.9
bar), adjust the span screw to achieve an output of
15.05 psig (1.1 bar)
10. Repeat steps 8 and 9 to verify and complete the
calibration.
Standard Performance: Full Range Input,
Reverse Action
Use the following procedure on reverse action units to
achieve a 15 to 3 psig (1.0 to 0.2 bar) output span for
a 4 to 20 mA input signal:
1. Perform steps 1 through 9 under Standard Perfor-
mance: Full Range Input, Direct Action, except for
step 2. In place of step 2, confirm that the unit is re-
verse acting. A red electronic circuit board identifies
reverse-acting units. Refer to Action under the head-
ing Electronic Circuit Board in Section 6 for more
information on reverse acting units.
2. Apply an input of 4.0 mA (Vm= 1.0 V), and adjust
the zero screw to achieve an output of 15.0 psig (1.0
bar).
3. Apply an input of 20.0 mA (Vm= 5.0 V), and adjust
the span screw to achieve an output of 3.0 psig (0.2
bar).
4. Repeat steps 2 and 3 to verify and complete the
calibration.
Multirange Performance: Full Range
Input(3), Reverse Action
Use the following procedure with a multirange unit to
achieve the desired reverse action output span for a 4
to 20 mA input signal:
1. Perform steps 1 through 9 of the calibration proce-
dure for Standard Performance: Full Range Input,
Direct Action, except for step 2. In place of step 2,
confirm that the unit is reverse acting. A red electronic
circuit board identifies reverse-acting units. Refer to
Action under the heading Electronic Circuit Board
in Section 6 for more information on reverse acting
units.
2. Apply an input of 4.0 mA (Vm= 1.0 V), and adjust
the zero screw to achieve the desired upper psi limit of
the output range. The 4 mA point must be between 9.0
psig (0.6 bar) and 30.0 psig (2.0 bar). The output in-
creases with clockwise rotation of the zero screw.
3. Apply an input of 20.0 mA (Vm= 5.0 V), and adjust
the span screw to achieve the desired lower psi limit of
the output range. The span must be at least 11.0 psi
(0.7 bar). The lower limit of the 20.0 mA setting is 0.5
psig (0.03 bar). The output increases with clockwise
rotation of the span screw.
4. Repeat steps 2 and 3 to verify and complete the
calibration.
Standard Performance: Split Range
Input, Reverse Action
4 to 12 mA Input Signal
Use the following procedure on reverse action units to
achieve a 15 to 3 psi (1.0 to 0.2 bar) output signal for
a 4 to 12 mA input signal:
1. Perform steps 1 through 9 of the calibration proce-
dure for Standard Performance: Full Range Input,
Direction Action, except for step 2. In place of step
2, confirm that the unit is reverse acting. A red elec-
tronic circuit board identifies reverse-acting units. Re-
fer to Action under the heading Electronic Circuit
Board in Section 6 for more information on reverse
acting units.
2. Apply an input of 4.0 mA (Vm= 1.0 V), and adjust
the zero screw to achieve an output of 15.0 psig (1.0
bar).
3. Apply an input of 12.0 mA (Vm= 3.0 V), and adjust
the span screw to achieve an output of 3.0 psig (0.2
bar).
4. Repeat steps 2 and 3 to verify and complete the
calibration.
12 to 20 mA Input Signal
Use the following procedure on reverse action units to
achieve a 15 to 3 psi (1.0 to 0.2 bar) output signal for
a 12 to 20 mA input signal:
Note
There may be some span interaction
with zero in this range, and the follow-
ing steps compensate for this.
1. Perform steps 1 through 9 of the calibration proce-
dure for Standard Performance: Full Range Input,
Direct Action, except for step 2. In place of step 2,
confirm that the unit is reverse action. A red electronic
circuit board identifies reverse-acting units. Refer to
Action under the heading Electronic Circuit Board
in Section 6 for more information on reverse acting
units.
2. Apply an input of 4.0 mA (Vm= 1.0 V), and adjust
the zero screw to achieve an output of 15.0 psig (1.0
bar).
3. Apply an input of 12.0 mA (Vm= 3.0 V), and adjust
the span screw to achieve an output of 3.0 psig (0.2
bar).

Type 846
3–4
4. Maintain the input of 12.0 mA (Vm= 3.0 V), and
adjust the zero screw to achieve an output of 15.0 psig
(1.0 bar). The unit may not turn up this high; if it does
not, go to step 7.
5. If the output reaches 15.0 psig in step 4, apply an
input of 20 mA, and adjust the span screw to achieve
a 3.0 psig output. Apply an input of 20 mA (Vm= 5.0
V), and note the error (the actual reading versus 3.0
psig). Adjust the span screw to overcorrect the error
by a factor of two. For example, if the reading was
2.95 psig, adjust the span screw to achieve an output
of 3.05 psig.
6. Repeat steps 4 and 5 to verify and complete the
calibration.
7. If the 12.0 mA (Vm= 3.0 V) cannot be adjusted to
15.0 psig (1.0 bar) in step 4, turn off the air supply.
Remove the module final assembly from the housing.
Place the range jumper in the L position for Low
Range, as shown in Figure 6-5. Replace the module
final assembly. Turn on the air supply.
8. Apply an input of 12.0 mA (Vm= 3.0 V), and adjust
the zero screw to achieve an output of 15.0 psig (1.0
bar).
9. Apply an input of 20 mA (Vm= 5.0 V), and note the
error (the actual reading versus 3.0 psig). Adjust the
span screw to overcorrect the error by a factor of two.
For example, if the reading was 2.95 psig, adjust the
span screw to achieve and output of 3.05 psig.
10. Repeat steps 8 and 9 to verify and complete the
calibration.
Transporting the Module Final Assembly
The design of the Type 846 allows the module final
assembly to be removed while the housing is in its
installed position. In the event the Type 846 does not
function properly, an operational module final assem-
bly can be taken to the field and exchanged with the
nonfunctional module.
After the Type 846 is calibrated in the shop, the mod-
ule final assembly can be removed from the housing.
At the time the span and zero screws disengage, there
will be minimal effect on the calibrated span. The cali-
brated module can now be taken to the field. Ensure
that the span and zero potentiometers are not moved
from their calibrated positions.

Type 846
4–1
Figure4-1. Type 846 Block Diagram
4 to 20 MA
INPUT
ELECTRONIC CIRCUIT
MAGNETIC ACTUATOR
PILOT STAGE
BOOSTER STAGE
SOLID-STATE
PRESSURE
SENSOR
3 TO 15 PSI
OUTPUT, TYPICAL
A6324/IL
Section 4
Principle of Operation
The following paragraphs describe the functional parts
of the Type 846. Figure 4-1 shows the block diagram.
Electronic Circuit
During operation, the input current signal is received
by the Type 846’s electronic circuit and compared to
the output pressure from the booster stage. A solid-
state pressure sensor is part of the electronic circuit
and monitors the booster stage output. The silicon-
based sensor uses strain gauge thin film technology.
The sensor’s pressure signal is fed to a simple internal
control circuit. By using this patented technique, the
Type 846’s performance is set by the sensor/circuit
combination. Changes in output load (leaks), varia-
tions in supply pressure, or even component wear are
sensed and corrected by the sensor/circuit combina-
tion. Electronic feedback allows crisp dynamic perfor-
mance and readily compensates for output changes
induced by vibration.
Note
Because the Type 846 is electronic in
nature, it is not well-modeled in the loop
as a simple resistor in series with an in-
ductor. Also it is better thought of as a
50-ohm resistor in series with a 6.0 V
voltage drop, with negligible induc-
tance.
Figure4-2. Detail of Deflector/Nozzle Pilot Stage
W6287/IL
This is important when calculating the loop load. When
the Type 846 is used in series with a microprocessor-
based transmitter, the noninductive nature of the Type
846 allows digital signals to successfully pass through
undistorted.
Magnetic Actuator
The electronic circuit controls the level of current flow-
ing through the actuator coil, which is located in the
pilot/actuator assembly. A change to the level of coil
current is made by the electronic circuit when it
senses a discrepancy between the pressure measured
by the sensor and the pressure required by the input
signal.
The actuator performs the task of converting electrical
energy (current) to motion. It uses a patented, coaxial
moving magnet design optimized for efficient operation
and is highly damped at its mechanical resonance. A
silicone rubber diaphragm protects its working mag-
netic gaps from contamination.
Pilot Stage
The patented pilot stage contains two opposed fixed
nozzles: the supply nozzle and the receiver nozzle. It
also contains the deflector, which is the moving ele-
ment. See Figures 4-2 and 4-3. The supply nozzle is
connected to the supply air and provides a high-veloc-
ity air stream. The receiver nozzle captures the air
stream and converts it back to pressure. The receiver
nozzle pressure is the output pressure of the pilot
stage.
To vary the pilot output pressure, the high-velocity
stream is diverted away from the receiver nozzle by
the deflector, which is a cylindrical, aerodynamic body
located between the two nozzles.
In response to a change in actuator coil current, the
deflector is repositioned between the nozzles. There is

Type 846
4–2
Figure4-3. Deflector/Nozzle Pilot Stage
Operation (Direct Action)
HIGHOUTPUTPRESSURE
PRESSURE TO
BOOSTER STAGE
REGULATED
AIR SUPPLY

DEFLECTED NOZZLE
FLOW PATTERN
PRESSURE TO
BOOSTER STAGE
REGULATED
AIR SUPPLY
A6645/IL
a linear relationship between the coil current and the
pilot stage output pressure. For direct action units the
power-off, or fail-safe, position of the top of the deflec-
tor is near the center of the stream and results in near-
ly zero pilot output pressure. As the coil is energized,
the deflector is drawn out of the stream.
For reverse action units, the power-off or fail-safe
position of the deflector is completely out of the
stream. The result is maximum pilot output pressure.
As the coil is energized, the deflector moves into the
stream, resulting in a decreased pilot output pressure.
The deflector material is tungsten carbide, and the
nozzles are 316 stainless steel. The nozzles have a
large bore of 0.016 inches (0.41 mm), which provides
good resistance to plugging.
Booster Stage
The receiver nozzle pressure controls the booster
stage, which has a poppet valve design. An increase
in receiver nozzle pressure positions the valving in the
booster stage to produce an increase in the transducer
output signal. A decrease in the receiver nozzle pres-
sure positions the valving in the booster stage to allow
exhaust to occur, decreasing the output signal.
The booster stage operates using a 3:1 pressure gain
from the pilot stage. High flow rate capability is
achieved by large flow area poppet design and internal
porting having low flow resistance. The booster stage
design provides very good stability in high vibration
applications, and the poppet valve technology provides
resistance to plugging.

Type 846
5–1
Section 5 Troubleshooting
The modular design and unitized subassemblies of the
Type 846 allows for quick and easy troubleshooting
and repair. This section presents information on the
diagnostic features and procedures for troubleshooting
the Type 846 in service or in the shop.
Diagnostic Features
If a control loop does not perform properly and the
cause of malfunction has not been determined, two
features of the Type 846 can be used to determine if
the transducer is at fault: the stroke port and Remote
Pressure Reading.
Stroke Port
The stroke port provides a way to quickly increase the
output of the Type 846, giving a rough measure of the
unit’s functionality. A hole in the module cover vents
the constant bleed from the pilot stage. When the hole
is covered, pressure at the pilot stage receiver nozzle
increases, which in turn increases the output. Output
pressure will increase to within 2 psi of supply pres-
sure for either direct or reverse action. If output pres-
sure does not increase to this level, it may indicate
that supply air is not reaching the pilot stage or that a
pilot stage nozzle is plugged.
Note
If the stroke port diagnostic feature is
not desired, the transducer is available
with an optional cover that contains
multiple stroke ports, as shown in figure
2-1. This prevents increasing the output
by covering the stroke port.
Remote Pressure Reading (RPR)
Remote Pressure Reading (RPR) is an optional diag-
nostic feature that enables the user to determine the
output pressure from any location along the signal wire
path. For loop troubleshooting, this allows the user to
confirm the functionality of the Type 846 from a re-
mote location.
A frequency signal directly proportional to the output
pressure is superimposed on the input signal loop.
The frequency range of the RPR function is 5,000 to
8,000 Hz.
A jumper on the circuit board activates the Remote
Pressure Reading function. Section 6–Maintenance
provides instruction on positioning the jumper. The
Figure5-1. HARTCommunicator ON/OFFKey
A6646/IL
Figure5-2. HARTCommunicatorMain Menu
A6647/IL
Figure5-3. HARTCommunicator Frequency Device Menu
A6648/IL
jumper, shown in Figure 6-5, has two positions: N for
ON, or D for OFF.
Using the HART Communicator to Read the RPR
Signal
Use the ON/OFF key to turn the HART Communicator
on and off. When the communicator is turned on, it
searches for a HART compatible device on the 4 to 20
mA loop. If a device is not found, then the communica-
tor displays the message, ‘‘No Device Found. Press
OK.’’ Press OK (F4) to display the Main menu.
If a HART-compatible device is found, the communica-
tor displays the Online menu.
When the HART Communicator is not connected to a
HART compatible device, the first menu to appear af-
ter powering is the Main menu.
From within the Main menu, you can access the Fre-
quency Device menu by pressing the 4key.
Using a Frequency Counter to Read the RPR Signal
A frequency counter also can be used for Remote
Pressure Reading. The frequency counter displays the
RPR output in the same manner as the HART commu-
nicator, but the output frequency must be converted to
output pressure using a simple mathematical formula.
To determine the output pressure, subtract 5,000 Hz

Type 846
5–2
Figure5-4. Wiring Connections for the HART Communicator or a Frequency Counter
CONTROLLER
POWER
SUPPLY
FREQUENCY
COUNTER
TEST
PINS
POSITIVE
NEGATIVE
GROUND
NOTE:
IF A HART COMMUNICATOR IS NOT AVAILABLE, A FREQUENCY COUNTER
CAN BE USED IN ITS PLACE. SEE TEXT TO CONVERT THE FREQUENCY DISPLAY
TO TYPE 846 OUTPUT PRESSURE
1
B2466/IL
from the frequency displayed on the frequency count-
er, and then divide by 100.
DisplayHz– 5,000 Hz
100
psig
5,311 Hz – 5,000 Hz
100 3.11
psig
Conversion Formula
Example:
Note
The Remote Pressure Reading (RPR)
frequency signal has an amplitude of 0.4
to 1.0 V peak-to-peak. If other noise (fre-
quency) with a comparable or greater
amplitude is present on the line, it may
make the RPR frequency signal unread-
able.
In-service Troubleshooting
A number of simple checks can be made on the Type
846 while the unit is in service. Figure 5–5 shows a
troubleshooting flowchart.
1. Make sure that the module cover is tight. The cover
should be hand–tightened and then advanced 1/4 to
1/2 turn (18 to 20 lbfSft) (24 to 27 NSm).
2. Confirm the general functionality of the unit by us-
ing the diagnostic features described earlier in this
section.
3. Confirm that the filter–regulator is not full of water
or oil and that supply air is reaching the unit. The air
supply pressure should be at least 3 psi (0.2 bar)
greater than the maximum calibrated output pressure.
4. Confirm that there are no major leaks in the output
signal line or from the output gauge port.
5. Confirm that there are no obstructions and the
screens are clean in the stroke port or the exhaust
port.
WARNING
An uncontrolled process may result in
death or serious injury. Unscrewing the
module cover removes power from the
electronics and the output signal will be
0.0 psi. Before removing the module
cover, ensure the device is properly
controlled.
WARNING
In explosive atmospheres, remove pow-
er and shut off the air supply to the
transducer before attempting to remove
the terminal compartment cover or mod-
ule cover. Failure to do so could result
in electrical spark or explosion.
6. For units with CENELEC Flameproof Certification,
remove the cover lock and screw to allow access to
the terminal compartment cover.
7. Remove the terminal compartment cover (see
Warning above), and use a milliammeter, or a digital

Type 846
5–3
Figure5-5. Type 846 Field TroubleshootingFlowchart
NOTE:
AFTER FINAL CORRECTIVE ACTION, CHECK LOOP OPERATION.
IF NOT OK, RESTART TROUBLESHOOTING PROCEDURE.
REFER TO REPLACING THE MODULE FINAL ASSEMBLY
IN SECTION 6.
1






C0789/IL
voltmeter to confirm that proper input current is sup-
plied to the transducer.
8. Remove the terminal compartment cover (see
Warning above), and short the loop across the positive
(+) and the negative (–) terminals to check the output.
The output should be nearly 0 psi. If the output is not 0
psi, replace the module final assembly.
9. Remove the terminal compartment cover (see
Warning above), and, using a digital voltmeter, check
the voltage between the positive (+) and negative (–)
terminals of the Type 846. The voltage should mea-
sure 6.0 to 8.2 V. A lower voltage can indicate a short
in the input wires or defective controller. No voltage
can indicate an open circuit in the control loop. A volt-
age of greater than 8.5 volts indicates a problem with
the Type 846, a faulty or corroded connection at the
transducer, or an overcurrent condition. Replace the
module final assembly. If the voltage is still not in the
proper range (6.0 to 8.2 V), remove the terminal block
and terminal block connection board. Apply power to
the electrical feedthroughs. (Note the polarity of the
feed–throughs, shown in Figure 6-9.) Recheck the
voltage. If the voltage is in the proper range, replace
the terminal block and terminal block connection

Type 846
5–4
board. If the voltage is still not in the proper range,
replace the housing.
10. Prepare to remove the module final assembly
from the housing, or to remove the Type 846 from its
mounting bracket. Refer to Module Final Assembly
in Section 6 for instructions on removing the module
final assembly from the module housing.
WARNING
An uncontrolled process may result in
death or serious injury. Unscrewing the
module cover removes power from the
electronics and the output signal will be
0.0 psig. Before removing the module
cover, ensure the device is properly
controlled
With the module final assembly removed from the
housing, the following checks can be made.
1. Review the position of the Remote Pressure Read-
ing jumper (if so equipped) and range jumper to con-
firm that they are placed in the desired position. Refer
to Electronic Circuit Board in Section 6, and Figure
6-5 for the location of these jumpers and instructions
on placement.
2. Observe the position and condition of the three
module O-rings to confirm they make a tight seal.
3. Verify that the O-ring is correctly positioned in the
groove on the flat face of the module cover. Refer to
Figure 6-9 for an exploded view.
4. Inspect the porting on the module final assembly to
determine if large amounts of contaminants have en-
tered the transducer.
Before making the following checks, disconnect both
signal wires from the Type 846, and ensure the mod-
ule final assembly is removed from the housing.
1. Using an ohmmeter, check the electrical connec-
tions in the housing terminal compartment. The circuit
should show an open between the positive (+) and
negative (–) terminals. If not, replace the housing or
terminal block and connection board.
2. Use a wire jumper to connect the two electrical
feedthroughs located in the module compartment. The
resistance between the positive (+) and negative (–)
terminals in the terminal compartment should be 10
ohms. If not, check the electrical feed–throughs for
short or open circuits. If a short or open circuit is
found, replace the housing.
3. With the electrical feed–throughs jumpered as
stated above, connect the ohmmeter to either the pos-
itive (+) or negative (–) terminal and the grounding lug.
The circuit should show an open. If not, check for a
short to the housing.
4. Remove the module from the module cover and
inspect the pilot/actuator assembly for damage or
clogging.
Some of the previous troubleshooting steps may be
inconvenient to perform in the field. It may be best to
make use of the modular design of the Type 846, and
keep a spare, calibrated module final assembly avail-
able for exchange. If the module final assembly is to
be transported to the shop for repair, first remove it
from the module cover. Attach the spare module final
assembly to the module cover. Refer to Module Final
Assembly in Section 6 for complete instructions. The
nonfunctioning module can then be returned to the
shop for troubleshooting.
Troubleshooting in the Shop
If the entire transducer is brought to the shop for trou-
bleshooting, then the preceding sequence applies. If
only the module final assembly has been brought to
the shop, then use another Type 846 housing as a test
fixture. Insert the module into the test fixture. Perform
the previous steps (as they apply) of the In-service
Troubleshooting procedure.
To further aid troubleshooting, the module final assem-
bly can be broken down into three subassemblies. The
troubleshooting sequence consists of exchanging the
subassemblies with known working ones to determine
which is at fault. The three subassemblies are the pi-
lot/actuator assembly, the electronic circuit board, and
the module subassembly. The module subassembly
consists of the module final assembly with both the
pilot/actuator assembly and electronic circuit board
removed.
1. Remove the pilot/actuator assembly. Refer to Pilot/
Actuator Assembly in Section 6 for complete remov-
al information.
a. Inspect the nozzles and deflector. If they show a
buildup of contaminants, clean the nozzles by
gently inserting a wire with a maximum diameter of
0.015 inches (0.38 mm). Clean the deflector, if nec-
essary, by spraying with LPSrElectro Contact
Cleaner.
CAUTION
Do not apply force to the deflector bar
while cleaning the nozzles. Doing so
could alter the alignment or disable the
deflector bar mechanism.