Dwyer Instruments Mini-Photohelic MP Series User manual

Series MP Mini-Photohelic®Differential Pressure Switch/Gage
Specications - Installation and Operating Instructions
Bulletin B-37-A
The Series MP Mini-Photohelic®Differential Pressure Switch/Gage combines
the time proven Minihelic®II differential pressure gage with two SPDT switching
setpoints. The Mini-Photohelic®is designed to measure and control positive, negative,
or differential pressures consisting of non-combustible and non-corrosive gases.
Gage reading is independent of switch operation. Switching status is visible by LED
indicators located on the front and rear of the gage.
SPECIFICATIONS
Service: Air and non-combustible, compatible gases.
Wetted Materials: Consult factory.
Accuracy: ±5% of full scale @ 70°F (21.1°C). Gage face mounted in vertical position.
Pressure Limits: 30 psig (2.067 bar).
Temperature Limits: 20 to 120ºF (-6.7 to 49°C).
Process Connections: Barbed for 3/16˝ I.D. tubing (STD); 1/8˝ male NPT (optional).
Size: 4-1/8˝ (104.78 mm) depth x 3-1/16˝ (77.79 mm) diameter.
Weight: 23 oz (652 g).
SWITCH SPECIFICATIONS
Switch Type: (2) SPDT relays.
Electrical Rating: 5A @ 120/240 VAC Resistive; 5A @ 30 VDC.
Electrical Connections: Screw Type Terminal Block. Accepts 22-12 AWG wire.
Power Requirements: 24 VDC / 24 VAC 50/60 Hz 4 watts.
Mounting Orientation: Gage face in vertical position.
Set Point Adjustment: Push Buttons.
Standard Accessories: (2) mounting screws, (1) .050˝ hex allen wrench.
Agency Approvals: cULus, CE.
LOW PRESSURE
PORT
HIGH PRESSURE
PORT 3-1/32 [77.00]
1 [25.4] 3-1/16
[77.79]
Ø2-19/32
[65.88]
3-13/16 [96.84]
3-1/32 [77.00]
9/32
[7.134]
®
DWYER INSTRUMENTS, INC.
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.
Phone: [phone]
Fax: [phone]
www.dwyer-inst.com
e-mail: [email protected]

INSTALLATION
1. Location: Select a location free from excessive vibration and where ambient
temperature will be between 20 to 120ºF (-6.7 to 49ºC). Pressure sensing lines
may be any length necessary without affecting accuracy. However, long runs of
tubing will dampen readings slightly and cause an increase in response time. If
pulsing pressure or vibration cause excessive pointer oscillation please contact
factory for ways to provide additional damping.
2. Position: The Mini-Photohelic®is calibrated and zeroed with gage face in the
vertical position at the factory. If the gage is used in any other position, it must
be re-zeroed each time the position is changed. Gages with ranges under 5 in. w.c.
(1.24 kPa), or equivalent, should be used only in the vertical position unless special
calibration was specied when ordering.
3. Mounting: The Mini-Photohelic®is normally mounted before making electrical
connections. Terminal blocks are located on the rear of the gage for electrical
connections.
a. Panel Mounting: Standard installation for the Mini-Photohelic®mounting
is ush through a panel. Allow approximately 1˝ clearance for pressure
tubing and electrical wiring. cut a 2-5/8˝ (66.68 mm) diameter hole in the
panel. Insert the Mini-Photohelic®into the panel, thread #6 mounting screws
into the mounting lugs and tighten.
Figure A
Figure B
4. Zeroing: Before installation, the Mini-Photohelic®may need to be zeroed before
placing into operation. If zeroing is required, you must rst remove the zero adjust
plug, located near the bottom face of the gage, with a small blade screwdriver.
(refer to Figure B.) The zero adjust screw is located directly behind the plug. Use
the hex allen wrench supplied and adjust until the pointer is on zero. This must be
done with both pressure connections vented to the atmosphere and the gage
oriented in the nal mounting position. Replace plug. Caution must be taken not to
overtighten the plastic plug when repluging.
5. Pneumatic Connections: To measure positive pressure, connect tubing to port
marked “+” and vent “–” port to atmosphere. For negative pressure (vacuum),
connect to port marked “–” and vent “+” port to atmosphere. If gage is supplied with
1/8˝ male NPT connections careful attention must be made not to over-tighten
ttings to avoid damage to the gage.
1 (25.40)
LOW
PRESSURE
PORT
HIGH
PRESSURE
PORT
2-19/32
(65.88)
3-1/16
(77.79)
1-7/16
(36.51)
2-3/8
(60.33)
23/64
(9.13)
1-15/16
(49.21)
11/64
(4.37)
5/32 (3.97)
MOUNTING HOLE
TYP 4 PLACES
2.276 (57.81) TYP
2-11/16 (68.26) SQ
ZERO ADJUST PLUG
PANEL MOUNTED
#6 MOUNTING
SCREW
MOUNTING
LUG
#4 MOUNTING
SCREW
#6 MOUNTING
SCREW
MOUNTING
LUG
REMOTE RELAY MOUNTED

6. Electrical Connections: Refer to Figure C for electrical connections located on
rear on Mini-Photohelic®Switch/Gage:
Section A contains external connections to the holding circuit for manual reset
applications. The function and use of these connections varies somewhat depending
on the circuit style of the instrument. See steps 7 and 9 for details.
Caution: Do not apply electrical current to terminals in Section A.
Section B contains the power connections for the control unit. Standard unit is
designed to operate on 24 VDC / 24 VAC 50/60 HZ.
Caution: Do not apply 120 / 240 VAC to the power connections.
Section C contains connections for SP1 and SP2 relays. Connections are marked on
the rear of the instrument.
7. Setpoint Calibration: Setpoint calibration is easily attained by actuating the push
buttons located on the rear of the instrument. Pushbuttons are labeled SP1 and
SP2. To set the setpoint SP1, apply pressure where you require the SP1 relay
to energize. Press pushbutton marked SP1 on the rear of the instrument, SP1
LED located on the front and rear of the instrument will ash several times. When
LED stops ashing calibration is complete. Repeat the same steps above for SP2
relay.
8. Circuit Style: The Mini-Photohelic®Switch/Gage is available with several factory
installed optional circuits. They are identied by the label shown in Figure D. This
label is mounted on the upper side of the main pressure housing.
The letter H denotes a circuit in which the relay can be made to latch or remain
energized after pressure increases above its setpoint.
The letter L denotes a circuit in which the relay can be made to latch or remain
de-energized after pressure decreases below its setpoint.
Two letters are required to fully identify a dual setpoint unit. Thus, circuit style
HH, which is standard, is a dual setpoint circuit which has provisions for latching
on pressure increase to either setpoint. Circuit styles may be used with either
setpoint stated above.
9. Dual Setpoint 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 C (Fig. C) for SP1 relay and SP2 relay. No connections are
required in Section A.
SECTION A
SECTION B
SECTION C
+
–
Figure C
Figure D
S1 SP1 Reset Terminal (Do not apply power)
S1 SP1 Reset Terminal (Do not apply power)
S2 SP2 Reset Terminal (Do not apply power)
S2 SP2 Reset Terminal (Do not apply power)
Vs 24 VDC / 24 VAC 50/60 HZ
Vs 24 VDC / 24 VAC 50/60 HZ
NO1 SP1 Relay NO Contact
C1 SP1 Relay Common Contact
NC1 SP1 Relay NC Contact
NO2 SP2 Relay NO Contact
C2 SP2 Relay Common Contact
NC2 SP2 Relay NC Contact
Section
A
Section
B
Section
C

Printed in U.S.A. 2/20 FR# 443249-10 Rev. 6©Copyright 2020 Dwyer Instruments, Inc.
DWYER INSTRUMENTS, INC.
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.
Phone: [phone]
Fax: [phone]
www.dwyer-inst.com
e-mail: [email protected]
10. Dual Setpoint Manual Reset: Circuit style HH may also be used for manual reset
applications where it is required to maintain contact on either relay following
pressure increase above its setpoint. Load or signal connections are made to
the appropriate terminals in Section C (as in step 8). Connect terminals in
Section A through normally closed switches or pushbuttons as shown in Figure E.
Use “dry-circuit” type switches such as Dwyer Part No. A-601 with palladium, gold,
etc. or rotary wiping action type contacts is recommended.
Circuit style LL is used for manual reset applications where it is required to
maintain contact on either relay following pressure decrease below the setpoint.
Load or signal connections are made to the appropriate terminals in section C (as
in step 8). A normally open type manual reset switch such as Dwyer Part No. A-601
is connected to the terminals in Section A. The circuit must be “armed” by
momentarily energizing the switch while the pointer is to the right of the setpoint.
From that point on, the circuit will latch on pressure decrease below the setpoint
and remain latched on pressure increase until manually reset with the optional
switch.
11. High Low Limit Control - Dual Setpoint: Standard circuit style HH may be used
to control various fans, dampers, pumps, etc..., between the setpoints of a Mini-
Photohelic®Switch/Gage. To accomplish this, use one setpoint relay to reset the
other as shown in the wiring diagram Figure F. In this typical application, the load
would be connected to the N.C. contacts (NC2) of the right setpoint relay SP2.
The N.O. contacts of SP1 relay would be connected to the S2 reset terminals
on the rear of the instrument. On pressure rise to the right setpoint relay SP2, the
relay would pull-in and hold even though the pressure might fall below that setpoint.
If the pressure continued to fall to the left of setpoint SP1, then SP2 relay would be
automatically DE-ENERGIZED, returning to its normal position and in so doing,
open the reset terminal S2. The right setpoint relay SP2 would thus be reset and
the cycle could repeat.
RESET
NC
NO
NO
NC
RESET
+
–
12. Dual Setpoint Special Purpose Circuits: Circuit Style LL may be used where
manual reset following maintained contact on pressure decrease to either
setpoint is required. Circuit HL and LH are combination units. For special
combinations of features and special units consult factory.
13. Failure Mode: The Mini-Photohelic®circuit design provides certain protection in
the event of a loss of electrical power. Both relays will de-energize upon loss of
power.
MAINTENANCE AND SERVICE
Dwyer Mini-Photohelic® Switch/Gages are precision instruments, expertly assembled
and calibrated at the factory. They require no lubrication or periodic servicing. If the
interior is protected from dust, dirt, corrosive gases and uids, years of trouble-free
service may be expected. Zero adjustment should be checked and reset occasionally
to maintain accuracy.
Upon nal installation of the Series MP Mini-Photohelic®Differential Pressure Switch/
Gage and the companion receiver, no routine maintenance is required. Aperiodic check
of the system calibration is recommended. The Series MP is not eld serviceable and
should be returned if repair is needed (eld repair should not be attempted and may
void warranty). Be sure to include a brief description of the problem plus any relevant
application notes. Contact customer service to receive a return goods authorization
number before shipping.
24 VDC/VAC
LOAD
+
–
Figure F
Figure E