Dwyer Instruments Model 1640 Floating Contact Null Switch for High and Low Actuation Installation and Operating Instructions

Bulletin E-50P7

2 [50.80]

Model 1640 Floating Contact Null Switch for High and Low Actuation

Specications - Installation and Operating Instructions

Model 1640 null switch.

The MODEL 1640 Floating Contact Null Switch is identical to Dwyer Large Diaphragm Pressure Switches, except for its electric switch. Model 1640 is

equipped with a single pole, double-throw oating 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 oating 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 pressure closes the “low” contact and causes

the motor to rotate in a clockwise direction. When the oating contact is in the null zone

there is no switching action and motor is at rest.

. Series 1630

Ø7-7/8

1/8 FEMALE

NPT LOW PRESSURE

CONNECTION

22.5°

1/8 FEMALE NPT HIGH PRESSURE CONNECTION

[76.20]

6-1/2 [165.10]

TYP

3-1/8 [79.37]

1/2 CONDUIT CONNECTION

Adjustment of the Switch: The “high” actuation point is indicated on a calibrated scale secured to the transparent range screw enclosure. Re-setting 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.)

1/2

[12.70]

TYP

3 [76.20]

4 [101.60]

Ø9/32 [7.14] MOUNTING HOLE TYP 4 PLACES

Adjusting the “null”.

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 oating 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.

TYP

21/32 [16.66]

Switching action in the Model 1640 null switch.

INSTRUMENTS, INC.

MODEL 1640 SWITCHES - OPERATING RANGES - NULL ZONE

Model

Number Range Inches, W.C. (Pa) 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 Specication

Differential pressure switches shall be diaphragm operated to actuate a single pole

double throw oating 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 oating contact switch shall be adjustable. Switches shall be Dwyer Instruments, Inc. Catalog No. ______ for the required operating ranges.

.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)

Adujustable Null Span

Min. Set Max. Set

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

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