Dwyer 1640 User Manual

Bulletin E-50P7

Model 1640 Floating Contact Null Switch for High and Low Actuation

Specifications - Installation and Operating Instructions

Model 1640 null switch.

The Model 1640 Floating Contact Null Switch is identical to Dwyer®.
Series 1630 Large Diaphragm Pressure Switches, except for its electric
switch. Model 1640 is equipped with a single pole, double-throw floating
contact switch (not snap action), so it functions as a null switch.

The drawing above shows the switching action schematically. As the
diaphragm moves in response to pressure changes, it moves the floating
contact to cause switching action at two preset points, with no switching
action between these points. The “high” circuit will be closed when rising
pressure differential reaches the preset level; the “low” circuit will be
closed when falling pressure differential reaches the preset level.

A typical usage for this switch is to position motorized dampers when sta­tic pressure in a duct system reaches a desired maximum, and to reposi­tion the dampers when the static pressure falls to a pre-established min­imum. By using a pitot tube sensing element, Model 1640 can serve in
the same way to control air velocity and maintain a constant volume of air
in a supply duct.

CAUTION: Because of the very low electrical rating, the 1640 switch is
almost always used with a relay which has suitable current carrying capa­bility.

Typical Wiring Hook-Up

Rising pressure closes the “high” contact which causes the motor to rotate
in a counterclockwise direction. Decreasing pressur e closes the “low” con­tact and causes the motor to rotate in a clockwise direction. When the
floating contact is in the null zone there is no switching action and motor
is at rest.

Switching action in the Model 1640 null switch.

Adjusting the “null”.

Adjustment of the Switch: The “high” actuation point is indicated on a
calibrated scale secured to the transparent range screw enclosure. Re­setting is accomplished by turning the adjustment screw with a screw­driver to the desired setting on scale. The “low” actuation point is set by
adjusting the span of the null by turning the Span Adjustment Screw on
top of the switch element inside the conduit enclosure. (See photo
above.)

SPECIFICATIONS
Ambient Temperature Range: -30°F (-34.4°C) for dry air or gas to

130°F (54.4°C).

Maximum Surge Pressure: 25 psig (172.4 kPa)
Rated Pressure: 10 psig (68.95 kPa)
Pressure Connections: 1/8” NPT
Electrical Ratings: Non-inductive — 2-1/2 amp, 110V A.C.; 1-1/2 amp,

220V A.C.; 1 amp, 24V D.C., 1/2 amp, 110V D.C., Inductive - 1 amp,
110V A.C.; 1/2 amp, 220V A.C.; 1/2 amp, 24V D.C. De-rate 70 - 80%
for very slow pressure changes.

Switch Action: SPDT floating contact (not snap action)
Wiring Connections: 3-screw type, common, high and low
Weight: 4 lbs., 13 oz. (2.18 kg)
Installation: Diaphragm vertical

CAUTION: For use only with air or compatible gases.

Model 1640 Switches - Operating Ranges - Null Zone

Model
Number

1640-0
1640-1
1640-2
1640-5
1640-10

NOTE: Special Models are available, including those with weather -proof or
explosion-proof enclosures.

Suggested Specification

Differential pressure switches shall be diaphragm operated to actuate a
single pole double throw floating contact “Null” switch. The pressure dif­ferential at which the electrical switch will be actuated on rising pressure
shall be adjustable. Set point adjustment shall be screw type with set point
indicated on a visual scale. The span of the floating contact switch shall be
adjustable. Switches shall be DwyerInstruments, Inc. Catalog No. ______
for the required operating ranges.

Range
Inches, W.C. (Pa)

.01 - 0.2
(2.482 - 49.77)

0.2 to 1.0
(49.77 - 248.8)

1.0 to 4.0

(248.8 - 995.3)

2.0 to 6.0
(497.7 - 1493)

3.0 to 12.0
(746.5 - 2986)

Adjustable
Min. Set

.01
(2.488)
.02
(4.977)
.03
(7.465)
.03
(7.465)
.04
(9.953)

Null Span
Max. Set

.03
(7.465)
.06
(14.93)
.12
(29.86)
.18
(44.79)
.20
(49.77)

©Copyright 2009 Dwyer Instruments, Inc. Printed in U.S.A. 7/09 FR# 23-440284-00 Rev. 2

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