Dwyer Instruments PHOTOHELIC 3000 SGT series Specifications-installation And Operating Instructions

SERIES 3000 SGT PHOTOHELIC

SNAP RING GROOVE

Ø4-3/4 [120.65]

MOUNTING HOLE

1/8 NPT FEMALE PNEUMATIC TAPS

2-1/16
[52.39]

2

[50.80]

PANEL 5/8 [15.88] MAX

1-1/4

[31.75]

3/16

[4.76]

5/8

[15.88]

2-1/2

[63.50]

3-7/8

[98.43]

5-1/8

[130.18]

4-3/8

[111.13]

HOUSING REMOVAL

3/4 [19.05]

CONDUIT OPENING

Ø4-3/4
[120.65]
FLANGE

3-7/8
[98.43] SQ
HOUSING

Ø4

[101.60]

FACE

5

[127.00]

0.D.

BEZEL

5-1/2

[139.70]

O.D.

MOUNTING

RING

Northeast Controls Incorporated
P.O. Box 275 - Upper Saddle River, New Jersey 07458 USA
Tel: [phone] | Fax: [phone] | [e-mail]

®

Bulletin B-36A

DIFFERENTIAL PRESSURE SWITCH/GAGE TRANSMITTER

Specifications – Installation and Operating Instructions

Fig. A

The PHOTOHELIC®Series 3000 SGT is a versatile 3-in-1

instrument combining a time-proven Magnehelic
pressure gage, low/high limit pressure switches and a 4-20 mA
pressure transmitter. It is designed to measure and control pos­itive, negative or differential pressure of air or other non-com­bustible, non-corrosive gases. Gage reading is unaffected by
switch or transmitter operation. Switch set points are easily
adjusted with knobs located on gage face. Applied pressure and
switch set points are fully visible at all times. Deadband is one
pointer width, less than 1% of full scale. Each set point controls
a DPDT relay and both can be interlocked to provide variable
deadband control. The 2-wire transmitter operates indepen­dently, driven by a separate external 10-35 VDC power supply.
Separate zero and span potentiometers are provided inside the
rear electronics package for easy field adjustment.

PHYSICAL DATA

Ambient Temperature Range: 20 to 120˚F (-6.7to 49˚C)
Maximum Pressure: Model No’s. 3020SGT & 3030SGT —

11psi (75 kPa); all other units 5psi (35 kPa).

Accuracy: ±2% of full scale at 70˚F (21.1˚C) (3% on -0).
Pressure Connections: 1/8˝ NPT(F)
Case FInish: Baked dark gray epoxy enamel
Conduit Opening: 3/4˝
Standard Accessories: (2) 3/16˝ tubing to 1/8˝ NPT brass adapters for

rubber or vinyl tubing, (1) mounting ring. (1) snap ring, (4) 6-32 x 2˝
mounting screws, instructions
Compatibility: Use only with air or other non-combustible, non-corro­sive gases

Weight: 4lbs., 12oz. (2.15 kg)

ELECTRICAL SPECIFICATIONS (Switches)

Power Supply: 117 VAC
Current Consumption: 5 watts average
Contact Rating: 10A @ 24 VDC or 120 VAC, 6A @ 240 VAC.

ELECTRICAL SPECIFICATIONS (Transmitter)

Power Supply: 10.0 to 35 VDC
Output Signal: 4-20 mA DC, 2-wire (limited at 38 mA)
Loop Resistance: 0-1250 ohms
Current Consumption: 38 mA DC, maximum
Span and Zero Adjustment: Multi-turn potentiometers,

internally accessible

Thermal Errors: ±1% per 50˚F typical
Warm-up Time: 10 minutes

®

differential

INSTALLATION

1. Location: Select a clean, dry, vibration-free location where

ambient temperatures will be between 20 and 120˚F (-6.7
and 49˚C). Tubing supplying pressure to the instrument can
be practically any length but long runs will increase response
time slightly.

2. Position: The PHOTOHELIC
use with scale in a vertical plane. Operation at other angles
may affect accuracy and/or require zero adjustment. Most
models can be specially calibrated at the factory for other
positions if specified at time of ordering. Ranges below 1˝
w.c. must be used only with scale vertical.

3. Mounting: Normal mounting is flush or through panel as
shown in Fig. B. Allow 4-3/8˝ space behind the unit for elec­trical enclosure removal. Make 4-3/4˝ diameter hole in panel.
When installing multiple units, it may be preferred to obtain a
Model 730E, 120mm chassis punch as manufactured by
Greenlee Tool Co. and available from your machine tool dis­tributor.

Insert PHOTOHELIC

®

ing ring over the case from rear and seat the snap ring in its
groove. Thread the (4) 6-32x2˝ machine screws into mount­ing ring, back it against snap ring and tighten screws to back
of panel. An alternative to flush mounting is the optional A­371 Surface Mounting Bracket. Unit is mounted in this
bracket as described above and bracket is then surface
mounted. Contact factory for details.

®

SGT is factory calibrated for

unit from front of panel, slip the mount-

Fig. B

4. Zeroing & Pneumatic Connections: After unit is installed in

COVER MOUNTING
SCREWS

FLEXIBLE CONDUIT

SUPPORT CONDUIT
FROM PANEL

SECTION B

SECTION A

SECTION C

SECTION D

SECTION E

its final mounting position, use the screw at bottom of front
cover to adjust pointer for exact zero reading. This must be
done with both pressure ports open and vented to atmos­phere.

(A) For positive pressure, connect tubing to HIGH PRESSURE

port and vent LOW PRESSURE port to atmosphere.

(B)For negative pressure (vacuum), connect tubing to LOW

PRESSURE port and vent HIGH PRESSURE port to atmos­phere.

When either port will be left open to atmosphere, we suggest
installation of optional A-331 Filter Vent Plug to keep gage
interior clean.

(C) For differential pressure, connect higher pressure to HIGH

PRESSURE port and lower pressure to LOW PRESSURE
PORT.

NOTE: If the PHOTOHELIC

®

SGT is over-pressured beyond
its full scale range, pointer could jump from full scale back to
zero and remain there until the excess pressure condition is
relieved. Users should be aware that this condition would
cause a false indication of zero pressure and subsequently
affect set-points and transmitter output signal.

Section E (L1 and L2) contains power supply connections for
the control unit transformer primary. The transformer in turn
supplies reduced voltage power for the LED, phototransistor,
amplifier unit, load relay pull-in and holding coils.
Connections must always be made to this section for the unit
to operate. Standard units require 117 VAC but options are
available for other power sources. See label on terminal
board for correct voltage and circuit style.

CAUTION: Do not apply electrical current to ter-

minals in Sections B and C.

Fig. D

Separate Ground Wire attachment is provided for by a No.

6-32 screw on the mounting bracket near the conduit open­ing.

SWITCH/GAGE WIRING CONNECTIONS

To make electrical connections, remove the (3) cover screws
and slide cover off. All wiring should be fed through flexible con­duit attached to conduit opening at bottom of electrical pack­age. Conduit should be attached to the panel of other suitable
support to avoid excess strain on the instrument. See Fig. C.

Fig. C

1. Low/High Set-Point Wiring Connections

The rear terminal board contains connections for low and
high set-points, holding coil circuits and line power supply.
Transmitter connections are located behind this terminal
board. See TRANSMITTER WIRING CONNECTIONS for
complete information.

Section A contains DPDT connections for the right or high
set-point and Section D contains identical connections for
the left or low set-point.

Terminals in Section B are for control of the holding coil cir­cuit for the right, high set-point and Section C contains iden­tical connections for the left, low set-point. These holding
coil circuits are typically used to allow latching set-points
with manual reset or for adjustable deadband operation with
one set-point wired to reset the other. See paragraphs 3 and
4 for details. Do Not Connect Line Current to Sections B or C.

2

Single Set-Point instruments are furnished with the right or
high set-point components and circuitry in place. These are
connected to Sections A and B of the terminal board. The left
or low set-point components are omitted.

2. Circuit Style: The PHOTOHELIC

®

is available with several
factory installed optional internal circuits. They are identified
as to style by a label shown in Fig. E. This label is mounted
prominently on the terminal board of each instrument. The
letter H denotes a circuit in which the relay can be made to
latch or remain energized after pressure increase to its set­point.

The letter L denotes a circuit in which the relay can be made
to latch or remain de-energized after pressure decreases to
its set-point. Two letters are required to fully identify a dual
set-point. Two letters are required to fully identify a dual set­point unit. Thus, circuit style HH, which is standard, is a dual
set-point circuit which has provisions for latching on pre­sure increase to either set-point. Single relay units are iden­tified by the letters SR followed by H for the standard unit or
L for the special low latch unit. Units for use with other than
standard 117 VAC will be so indicated on the label.

Fig. E

3. Dual Set Point Automatic Reset: Circuit Style HH is used

for simple on-off switching applications. To place in service,
connect load circuits to the appropriate terminals in Section
A (Fig. D) for the right set-point and Section D for the left set­point. Note that the N.O. contacts are open when the gage
pressure pointer is to the left of the set-pointers. No connec­tions are necessary in Sections B and C. Make external
ground connections as required and connect power to
Section E for the control unit. To use circuit style LL for auto­matic reset, a jumper wire must be installed between the
upper and lower terminals in Sections B and/or C.

4. Dual Set Point Manual Reset: Circuit Style HH may also be

RESET

NC

NO

RESET

NC

NO

HI LO

C

NO NC NC NO C

C

NO

NC NC NOC

L

2

L

1

1/3 HP*

120 V
LOAD

RESET JUMPERS

Northeast Controls Incorporated
P.O. Box 275 - Upper Saddle River, New Jersey 07458 USA
Tel: [phone] | Fax: [phone] | [e-mail]

used for manual reset applications where it is desired to have
maintained contact on either relay following pressure
increase above its set-point. Load or signal connections are
made to the appropriate terminals in Sections A and D (as in
paragraph 3 above). Connect terminals in Sections B and C
through normally closed switches or push buttons as shown
in Fig. F. Use of “dry-circuit” type switches such as Dwyer
Part No. A-601 with paladium, gold, etc. or rotary wiping
action type contacts is recommended. Make external ground
connections as required and connect power to Section E for
the control unit.

Circuit style LL is used for manual reset applications which
require that contact be maintained following pressure
decrease below the set-point. Load connections are made to
the appropriate terminals in Sections A and D. A normally
open type manual reset switch such as Dwyer Part No. A-601
is connected to the terminals in Sections B and C. The circuit
must be reset or “armed” by momentarily closing the switch
while the black pointer is to the right of the set-point. From
that point on, the circuit will latch on pressure decrease
below the set-point and remain latched on pressure increase
until manually reset with the optional switch.

★

Note: For larger motors, use the Photohelic®in a main-

tained contact, 120 Volt Control or Push Button Circuit of

the motor starter.

Fig. G

7. Dual Set-Point Special Purpose Circuits: Circuit Style LL

may be used where manual reset following maintained con­tact on pressure decrease to either set-point is desired.
Circuit Styles HL and LH are combination units. For special
combinations of features, special units, and detailed instruc­tions regarding their use, consult the factory.

8. Single Set-Point PHOTOHELIC

PHOTOHELIC

®

is furnished with the right set-point only.

®

: The single set-point

Terminals in Sections A and B (Fig. D) are connected to this
relay. Circuit Style SRH is wired for automatic reset as in
paragraph 3 above. Manual reset is accomplished by adding
a normally closed reset switch or push button to the circuit
as described in paragraph 4 above.

CAUTION: Do not apply electrical current to

terminals in Sections B and C.

Manual Reset with Circuit HH

Fig. F

5. Dual Set Point Automatic and Manual Reset Combinations:

Circuit style HH may be used with either set-point wired and
operating with automatic reset as described in paragraph 3
above and other set-point wired and operating with manual
reset as described in paragraph 4.

6. High Low Limit Control – Dual Set-Point: Circuit Style HH
may be used to control fans, dampers, pumps, etc., between
the set-points of a PHOTOHELIC
one set-point relay to reset the other as shown in the wiring
diagram Fig. G. In this typical application, the load (for

®

. To accomplish this, use

instance a fan) would be connected to the N.C. contacts of
the right set-point relay, Section A (Fig. D). On pressure rise
to the right set-point, its relay would pull in and hold even
though pressure might then fall below that set-point. If the
pressure continued to fall to the left set-point, its relay would
automatically be DE-ENERGIZED, returned to its normal
position and in so doing, open the holding coil circuit from
Section B (Fig. D). The right set-point relay would thus be
reset and the cycle could repeat.

9. Single Set-Point Special: Manual reset after actuation on
falling pressure can be obtained by using Circuit Style SRL.
Consult the factory for special units and detailed instructions
regarding their use.

10. Placing in Service: In normal operation each relay is de­energized when the pressure applied to the instrument is
below its set-point. Special low-latching units will ordinarily
have to be reset before placing on the line in normal opera­tion.

11. Failure Mode: The PHOTOHELIC

®

circuit design provides
certain protection in the event of a loss of pressure or elec­trical power. In either case, both relays will de-energize,
returning to their normal “zero pressure” state. The excep­tions to this are models with center zero ranges. Because the
relays on all standard models are always ener gized when the
indicating (black) pointer is to the right of their respective set
points, the relay action on loss of pressure will depend on
set-point position, since either of them could be located to
the left of zero. As an example; if the left pointer were set at

-2 in. w.c. and negative pressur e was -3 in w .c., a loss of that
pressure would allow the black pointer to return to the cen­ter and thus cause the low set-point relay to energize.

If the LED should burn out, only the left-low relay will de­energize. The right-high relay will react as if pressure were
above its set-point and will remain energized even though
pressure might be below that setting. In this situation, only
termination of electrical power will allow the right-high relay to
de-energize.

3

TRANSMITTER WIRING CONNECTIONS

POSITIVE

NEGATIVE

SERIES

3000 SGT

PRESSURE

TRANSMITTER

RECEIVER

POWER
SUPPLY

10-35 VDC

SPAN ZERO

MAXIMUM VALUE (1250Ω)

RL MAX. = Vps-10.0

20 mA DC

OPERATING
REGION

1500
1400
1300
1200
1100

1000

900
800
700
600
500
400
300
200
100

50

TOTAL RECEIVER RESISTANCE (

Ω)

05

10 13 15 20 25 30 35 40

VDC

Northeast Controls Incorporated

P.O. Box 275 - Upper Saddle River, New Jersey 07458 USA

Tel: [phone] | Fax: [phone] | [e-mail]

Electrical connections for the two-wire, 4-20 mA transmitter cir­cuit are made to the small terminal block mounted behind the
larger switch/gage terminal board. Wiring should enter this area
through the 5/8″ dia. hole at bottom of electronics chassis. See
Fig. H.

Fig. H

The transmitter function of the PHOTOHELIC
independent of the low/high switch set-points and requires a
separate external power supply delivering 10.0 to 35 VDC with
minimum current capability of 40mA to power its control loop.
Refer to Fig. J for connection of the power supply, transmitter
and receiver. The range of appropriate receiver load resistance
(R

) values for various power supply voltages is defined by the

L

formula and graph in Fig. K. Shielded two wire cable is recom­mended for control loop wiring and the negative side of the loop
can be grounded if proffered. The receiver can be connected in
either the positive or negative side of the loop. If the polarity of
the transmitter or receiver is inadvertently reversed, the loop will
not function properly but no damage will be done to the trans­mitter.

®

SGT operates

Voltage Input

The PHOTOHELIC

®

SGT Transmitter can easily be adapted for
receivers requiring 1-5 VDC input. Insert a 250 ohm, 1/2 watt
resistor in series with the current loop but parallel to the receiv­er input. Locate this resistor as close as possible to the receiv­er input. Because resistor accuracy directly influences output
signal accuracy, we recommend use of a precision ±0.1% toler­ance resistor to minimize this effect.

Transmitter Output Calibration

Each unit is factory calibrated to produce 4mA DC of loop cur­rent at zero pressure and 20mA DC at full scale. To check cali­bration use the following procedure.

1. Connect a controllable source of pressure to the high pres-

sure port and leave the low pressure port vented to atmos
phere.

2. With transmitter connected to its companion receiver and

power supply, insert an accurate milliameter ranged to
approximately 30 mA in series with the current loop.

3. Apply electrical power to the system and check for proper

operation. Slowly apply pressure and confirm that loop cur­rent increases above the 4 mA zero pressure value.

4. Span and zero controls are located behind the terminal board

as shown in Fig. L. Apply pressure until gage reads full scale
and adjust span control for 20 mA loop current.

The maximum wire length between the transmitter and receiver

Fig. L

is a function of wire size and receiver resistance. Connecting
wires should not contribute more than 10% of the receiver resis­tance to total current loop resistance. Where long runs (over
1,000 feet) are required, select receivers with higher resistances
to minimize size and thus cost of wiring. For runs up to 100 feet,
wire as small as 24 AWG can be used.

5. Relieve pressure and adjust the zero control for a reading of 4

mA loop current.

6. Zero and span controls are slightly interactive so steps 4 and 5

should be repeated until outputs are consistently 4 and
20mA, respectively.

7. Remove the milliameter from the current loop, make connec-

NOTE: RECEIVER MAY BE IN SERIES WITH

+ OR - LEG OF CONTROL LOOP

tions to system pressure sources and place unit in service.

Multiple Receiver Installation

An advantage of the standard 4-20 mA DC output signal used in
Series 3000 SGT switch/gage/transmitters is the compatibility
with a wide range of receivers. Devices such as the A-701
Digital Readout, a chart recorder and other process control
equipment can all be operated simultaneously. It is only neces­sary that all devices be designed for a standard 4-20 mA DC

Fig. J

input, the proper polarity of input connections be observed and
the combined receiver resistances not exceed the maximum for
the current loop. If any receiver indicates a negative or down­scale reading, the signal input leads are reversed.

Maintenance

After final installation of the PHOTOHELIC

®

Switch/gage/trans­mitter no routine maintenance is necessary. A periodic check of
calibration is recommended following the procedure under
TRANSMITTER OUTPUT CALIBRATION. Otherwise, these units

©Copyright 2000 Dwyer Instruments, Inc. Printed in U.S.A. 11/00 FR#13-440202-05 Rev.1

Fig. K

are not field repairable and should be returned, freight prepaid,
to the following address if service is necessary. Be sure to
include a brief description of the problem plus any relative appli­cation information available.

Dwyer Instruments, Inc.
Attn: Repair Department
102 Highway 212
Michigan City, IN 46360