The letter “L” denotes a circuit in which the relay can be
made to latch or remain de-energized after pressure
decrease to its set-point. Two letters are required to fully
identify a dual set-point unit. Thus, circuit style HH, which is
standard, is a dual set-point circuit which has provisions for
latching on pressure 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.
5. Dual Set Point Automatic Reset
Circuit Style HH is used for simple on-off switching applica-
tions. To place in service, connect load circuits to the appro-
priate terminals in Section A (Fig. 6) for the right set-point
and Section D for the left set-point. Note the the N.O. con-
tacts are open when the gage pressure pointer is to the left
of the set-point pointers. No connections are necessary in
Section 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.
6. Dual Set Point Manual Reset
Circuit Style HH may also be used for manual reset applica-
tions 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 ter-
minals in Sections A and D (as in paragraph above).
Connect terminals in Sections B and C through normally
closed switches or push buttons as shown in Fig. 8. Use of
“dry-circuit” type switches such as Dwyer Part No. A-601
with paladium, gold, etc. or rotary wiping action type con-
tacts 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 normal-
ly 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 “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 and 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®. To
accomplish this, use one set-point relay to reset the other as
shown in the wiring diagram Fig. 9. In this typical applica-
tion, the load (for instance a fan) would be connected to the
N.C. contacts of the right set-point relay, Section A (Fig. 6)/
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, its relay would automatically be De-Energized,
return to its normal position and in so doing, open the hold-
ing coil circuit from Section B (Fig. 6). 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 desired. Circuit Styles HL and LH are combination units.
For special combinations of features, special units, and
detailed instructions regarding their use, consult factory.
10. Single Set-Point Photohelic®
The single set-point photohelic®is furnished with the right
set-point only. Terminals in Section A and B (Fig. 6) are con-
nected to this relay. Circuit Style SRH is wired or automatic
reset as in paragraph 5. Manual reset is accomplished by
adding a normally closed reset switch or push button to the
circuit as described in paragraph 6.
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.