Condition Sensing Switches and Controls

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Speed Sensing

Technical Data

Theory of Operation

When the shaft of a speed switch is rotated, a magnetic induction linkage operates a contact. One contact is provided for clockwise operation, and one contact for counterclockwise operation. See Figure 1 for a simplified view of the operating mechanism of a Speed Switch with normally open contacts. Operation of a device with normally closed contacts is similar.

When the shaft (1) rotates, the field of the magnet (2) induces eddy currents in the copper cup (3). These currents produce an electromagnetic torque proportional to the shaft speed, which produces a rotational torque on the cup in the same direction as the shaft rotation. The cup engages a contact operating lever (4) to activate the contacts.

As the shaft speed increases, the operating torque will also increase. When the torque has increased enough to overcome an opposing adjustable spring force (5), the moveable contact (6) is forced against the stationary contact (7). The contacts close and will remain closed as the shaft speed increases to its normal value.

Similarly, as the shaft speed is decreased, a speed is reached where the spring force again exceeds the operating torque and the contacts return to their normal position.

As the shaft speed increases, the contact set speed (the speed at which the contacts operate) will be at a higher RPM than the speed where the contacts reset (return to their normal position) on decreasing RPM. The difference in these contact operating values is called the differential.

Ambient Temperature Range

Temperatures below 32°F (0°C) are based on the absence of freezing moisture, water, or other fluids that may solidify and impede contact operation of the control. Temperature ranges are as follows:

Operating: –22…150°F (–30…66°C)
Storage: –22…200°F (–30…93°C)

Typical Control Circuits

Forward Plugging — Circuit shown in Figure 2 is a typical control circuit for forward direction plugging with optional lockout protection. Operation is as follows:

        Pushing START energizes the forward coil and closes normally open contact F1; the motor runs forward. Normally closed contact F2 opens the circuit so the reverse coil does not energize. The forward contact on the speed switch closes. Pushing STOP drops out the forward contact. Then the reverse contactor or starter is energized and the motor is plugged. When the motor speed decreases to the preset speed setting of the speed switch, the contact opens and drops out the reverse contactor.

Conveyor Sequencing — Circuit shown in Figure 2 is a control circuit for conveyor sequencing. Operation is as follows:

        Pushing START energizes coil M1 to start the first conveyor and closes the normally open contact. When the first conveyor reaches the preset speed setting of the speed switch, the speed switch contact closes, energizing coil M2 to start the second conveyor. Pushing STOP drops out coils M1 and M2, stopping the conveyors.

Anti-Plugging — Circuit shown in Figure 2 is a typical anti-plugging control circuit. The circuit is used where damage would result from a sudden reversal of power. Bulletin 808 contacts keep the reverse circuit open until the motor has coasted to a preset speed.

Figure 1
Operating Mechanism



Figure 2
Typical Control Circuits



Lockout Solenoid

In some applications, an accidental turn of the shaft may close the Bulletin 808 contacts that jog or start the motor. To guard against this, the Bulletin 808 can be equipped with a lockout solenoid, which mechanically restrains the contacts from operating unless the lockout coil is energized. This feature is available factory-mounted or in kit form. To order Lockout Solenoid, see Modifications and Accessories.

Mounting

The Type 1, 4 & 13 enclosure is available in three types of mounting brackets. They are base mounting, 3-point flange mounting and 4-point flange mounting. These devices are also available without mounting bracket for direct mounting. The Type 7 & 9 enclosure is available with base mounting only. Mounting brackets can be assembled at the factory, or ordered separately as accessories.

Installation

For greatest accuracy, the Bulletin 808 shaft should be driven at the highest available speed within its maximum operating speed. It is recommended that the continuous driven speed be at least two times the speed at which the contacts are set to operate. This will provide the torque to hold the contacts in the desired position, reducing false contact operation under severe shock and vibration. The driven speed can be higher than the adjustable range speed, but must not exceed the maximum shaft operating speed. There must be a positive coupling between the Bulletin 808 and machine. A rigid coupling should not be used. However, flexible couplings are recommended and available from local Power Transmission Equipment Distributors. Gears, chains, or timing belts can be used if it is not possible to mount a flexible coupling. A V-belt is not recommended for plugging applications.

Adjustment

The contact operating speed is easily adjusted with two external adjustment screws, one for each set of contacts. After the speed switch has reached normal operating temperature, the screw is turned to adjust the contact operating speed. Changes in inertia (WR²) of moving equipment may require readjustment of the set points.

Shaft Loading

If the radial and axial shaft loading values are exceeded, shortened bearing life may result. The maximum values are listed in the Maximum Shaft Loading table below. In speed sensing or direction of motion applications, a timing belt may be used. A V-belt is not recommended. Proper belt tension must be maintained to keep slippage at a minimum.

Maximum Shaft Loading

Enclosure	Maximum Radial Loads	Maximum Axial Loads (Thrust Loads)
Type 1, 4 & 13	50 lbs. (222 Newtons)	20 lbs. (89 Newtons)
Type 7 & 9	25 lbs. (111 Newtons)	20 lbs. (89 Newtons)
Note:Timing belt tension must not exceed 25 lbs. (111 Newtons).

Typical Torque and Temperature Rise Characteristics

Contact Operating Range RPM	Shaft Operating Speed Maximum RPM	Driving Torque Maximum lb•in	Temperature Rise (Maximum RPM) °F
15…80	1200	6 (.68 N•m)	120 °F (49 °C)
50…1000	2000	6 (.68 N•m)	140 °F (60 °C)

Contact Ratings — NEMA B600

AC						DC
Maximum AC Voltage	Amperes		Continuous Carrying Current	Voltamperes		Maximum Voltage	Ampere
	Make	Break		Make	Break
120	30	3.00	5	3600	360	115…125 230…250	0.12 0.08
240	15	1.50	5	3600	360
480	7.5	0.75	5	3600	360
600	6	0.6	5	3600	360	—	—

Contact Wiring Configurations