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.