11. 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.
12. Placing in Service: In normal operation each relay is de-energized 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.
13. Failure Mode: The PHOTOHELIC®Switch/Gage 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 energized 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 pressure 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 de-energize. 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.
MAINTENANCE
Dwyer Instruments, Inc. 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. The PHOTOHELIC®Switch/Gage 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 (RGA) number before shipping.
©Copyright 2017 Dwyer Instruments, Inc. Printed in U.S.A. 1/17 FR# 440202-04 Rev. 6
DWYER INSTRUMENTS, INC.
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®Instruments, Inc. Part No. A-601 is connected to the
terminals in Sections B and C. The circuit must be “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.
7. Dual Set Point Automatic and Manual Reset Combinations: Circuit Style HH
may be used with either set point wired and operating as in paragraph 5 above and the
other set point wired and operating as in paragraph 6.
8. 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®Switch/
Gage. To accomplish this, use one set point relay to reset the other as shown in the
wiring diagram Figure M. In this typical application, the load (for instance a fan) would
be connected to the N.C. contacts for the right set point relay Section A (Figure J).
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. I the pressure continued to fall to the
left set point, its relay would automatically be DE-ENERGIZED, return to its normal
position and in so doing, open the holding coil circuit from Section B (Figure J). The
right set point relay would thus be reset and the cycle could repeat.
9. 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 required. Circuit Styles HL and LH are combination units. For special combinations
of features, special units, and detailed instructions regarding their use, consult the
factory.
10. Single Set Point PHOTOHELIC®:The single set point PHOTOHELIC®Switch/
Gage is furnished with the right set point only. Terminals in Sections A and B (Figure
J) are connected to this relay. Circuit Style SRH is wired for automatic reset as in
paragraph 5 above. Manual reset is accomplished by adding a normally closed reset
switch or push button to the circuit as described in paragraph 6 above.
NC
NO
NC
NO
HI LO
CNO NC NC NO C
C
NO NC NC NOC
L2 L1
1/3 HP*
120 V
LOAD
HI LO
CNONCNC NO C
C
NO NC NC NOC
L2 L1
Figure L Figure M
CAUTION: Do not apply electrical current to
terminals in Sections B and C.
Manual Reset with Circuit HH
*Note: For larger motors, use the Photohelic®
Switch/Gage in a maintained contact, 120 Volt
Control or Push Button Circuit of the motor starter.
