US2339581A - Timing of electromagnetic switches - Google Patents

Description

A. W. PAULSON ETAL TIMING 0F ELECTROMAGNETIC SWITCHES Jan. 18, 1944.

Filed Jan. 8, 1942 03 }INVENTOR5 "av/Min ATTO RNEY Patented Jan. 18,1944

TIMING OF ELECTROMAGNETIC SWITCHES Arthur Willard Paulson, Yonkers, and William Henry Bruns, Lincolndale, N. Y., assignors to Otis Elevator Company, New York, N. Y., a corporation of New Jersey Application January 8, 1942, Serial No. 426,042

9 Claims.

The invention relates to the timing of electromagnetic switches.

There are various direct current control circuits for electromagnetic switches in which condensers are utilized for timing the operation of the switches. In some arrangements the condensers are utilized to time the going in of the.

switch, in others the dropping out of the switch and in still others to time both the going in and dropping out of the switch. It is important not only that accurate and uniform timing be obtained but also that the cost of'various items employed be kept at a minimum. Paper condensers are relatively expensive while electrolytic condensers are unreliable in timing under conditions when the length oftime that the condenser is discharged is considerable and varies.

One feature of the invention resides in a timing arrangement in which the parts are simple and inexpensive.

Another feature of the invention resides in the provision of a timing circuit for an electromagnetic switch in which accurate and uniform timing may be obtained utilizing an electrolytic condenser.

Other features and advantages of the invention will become apparent from the following description and appended claims.

In carrying out the invention according to the arrangement which will be described, the timing condenser is in a charged state when the electromagnetic switch controlled thereby is not operated. To operate the switch, a circuit is completed to cause a magnetizing force to be exerted for operating the switch. At the same time, the condenser is connected to cause by its discharge a magnetizing force to be exerted to delay the operation of the switch. In the case of certain types of switches, aresistance may be provided which is short circuited when the switch contacts engage to increase the operating magnetiz-- ing force to pull the switch to full operated position. This enables a smaller condenser to be utilized with such switch to obtain the desired timing. In dropping out the switch, the condenser may be recharged by a circuit which causes sufficient magnetizing force to be exerted to maintain the switch operated until the charging current decreases to a certain value. If desired, the condenser may be recharged without aflecting the operation of the switch, in which event the switch is dropped out immediately and the charging is efiected quickly in preparation for a subsequent operation.

The single figure of drawing is a' wiring diagram of a simple circuit illustrating the control of a switch in accordance with the invention.

The switch to be controlled is designated A. The coil of this switch is connected in series with condenser across the supply lines and This coil is tapped to provide two portions designated Aa and Ab. An electromagnetic switch B is provided for connecting the portion Ab of the switch coil across the supply lines by a circuit I0 which also connects the condenser C across the portion Ad of the coil. The construction of the switch is such that the portion Ab alone when connected across the supply lines is capable of operating the switch. For convenience the coil of switch B is illustrated as controlled by manually operable switch H. Resistance RI is a pro-' tective resistance for the condenser. Resistance R2 is to facilitate obtaining the desired ampere turns of coil portion Aa. Resistance R3 serves to facilitate providing the desired number of ampere turns of coil portion Ab without undue heating. Resistance R4 is for adjusting the time of operation. 'It is preferred to employ a separate protective resistance RI especially where several condensers are employed in parallel as this permits each condenser to have its own protective resistance. However, where only one condenser is utilized as illustrated, resistance RI may be omitted and the right hand side of contacts Bl connected between the coil of switch A and re-' sistance R3, thereby utilizing resistance R3 also as a protective resistance.

With switch B deenergized,. the condenser is charged with the voltage of the supply lines while the voltage applied to the coil of switch A is zero.

To operate switch A, manual switch II is closed causing the energization of the coil of switch B. Switch B operates to separate contacts B I, breaking the shunt circuit for the coil of switch A and resistances R2, R3 and R4. It also engages contacts B2 which connect portion Ab of the coil of I switch A across the supply lines in circuit with resistances R3 and R4. The closing of these contion Ab of the coil. I This prevents the immedi 1 ate operation of the-switch. The condenser discharges until a point is reached where the magnetizing force of coil portion Aa becomes low enoughto permit coil portion Ab to operate the resistance RI being of a relatively low value.

The ampere turns of the portions of the coil of switch A, the capacity of the condenser and the value of resistance R2 and the resistance of coil portion Aa are so coordinated and the value of resistance R4 is so adjusted as to cause the switch to operate at the expiration of the desired time interval. With a given rate of discharge of the condenser, the time of operation of the switch may be adjusted by adjusting the value of resistance R4.

When switch A operates it engages 'contacts'Al to short circuit resistance R4. This arrangement is particularly desirable where switch A is a power switch, as for example having'contacts in the lines from a power supply to a motor. Such contacts have strong contact springs which after the contacts engage must be compressed as the switch is pulled all the way in. This requires a larger number of ampere turns in the coil portion Ab. By utilizing auxiliary contacts AI of the switch to short circuit resistance R4 at the time the contacts engage, the current is increased in coil portion Ab to a point sufiicient to pull the switch into fully operated position against the contact springs. A given size condenser may be utilized to provide the same time of operation of a switch with heavy contact springs where contacts Al are utilized as of a switch without such springs andwithout utilizing contacts Al. Thus, contacts Al may be omitted where the switch does not have to pull all the way home against rela-- tively strong contact springs.

To drop out switch A, switch I I is opened causing the deenergization of switch B. Switch B upon dropping out separates contacts 252 to break circuit l0, disconnecting coil'portion Ab of switch A from the line and opening the bypass for the condenser and coil portion Aa. Switch B also reengages contacts BI which connects the condenser directly to the supply lines through resistance RI. Thus condenser C recharges immediately and there is no tendency for coil of switch A to hold the switch in operated condition. Therefore, switch A drops out immediately.

If it be desired to delay the dropping out of switch A, the circuit through contacts BI is omitted in which event, upon the dropping out of switch B, the condenser recharges through the coil of switch A. Thus the resistance of the coil of switch A, resistance R2 and also resistance R4, where contacts Al are not provided, delay the charging of the condenser so that sufilcient current flows through the coil of switch A to maintain the switch operated. As soon as the condenser charges to a certain point this current fiow is no longer suflicient to hold switch A operated and it drops out.

The above described arrangement is especially suitable for controlling the operation of accelerating switches, say for an elevator hoisting motor. In such case switch B might be a switch which operates to connect the motor to the supply lines or operates the same time such connection is effected, whereas switch A might be the first accelerating switch. In such event contacts A2 and A3 may be utilized to control the operation of a second accelerating switch in the same manner as contacts BI and B2 respectively of switch B control the operation of switch A. Contacts A4 would then be utilized to control a work circuit such as effecting the short circuiting of a resistance step in circuit with the motor. It is to be understood that the application of the above arrangement to controlling the operation of one or more accelerating switches is only illustrative and that the arrangement may be utilized for various other purposes.

It is seen therefore that the timing of the operation of a switch is controlled in a very simple and reliable manner by the discharge of a condenser to create a magnetizing force in opposition to the operating magnetizing force. Also a very simple and reliable control of the timingof the dropping out of a switch is effected by utiliz-' It is to be understood that in applying'the invention to various control systems, changes may be made with a view to adapting the invention more readily to such systems. Other changes may also be made which do not depart from the spirit and scope of the invention. It is therefore intended that all matter contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electromagnetic switch having two coil portions, a condenser, means including a direct current source of supply for causing said condenser to be in a charged state and both coil portions deenergized when the switch is not operated, I

and means for causing excitation of one of said coil portions sufilcient'to operate said switch and for connecting said condenser across the other coil portion to cause through the discharge of the condenser excitation of said other coil portion so as to delay the operation of the switch.

2. An electromagnetic switch having two coil portions, a condenser, means including a direct current source of supply for causing said condenser to be in a charged state when the switch is not operated, and means for causing excitation ofone of said coil portions sufilcient to operate said switch and for at the same time connecting said condenser across the other of said coil portions to cause through the discharge of the condenser a magnetizing force to be exerted by said other coil portion in opposition to the magnetizing force exerted by said one coil portion sufiicient to delay the operation of the switch until the condenser discharges to a certain voltage.

3. An electromagnetic switch having two coil portions, a source of direct current, a condenser connected to said source so as to be in a charged state when the switch is not operated, and means for connecting to said source one of said coil portions to cause suflicient magnetizing force to be exerted thereby for operating said switch and for at the same time connecting said condenser across the other of said coil portions to cause through the discharge of the condenser magnetizing force to be exerted by said other coil portion in opposition to the magnetizing force exerted by said one coil portion to delay the operation of the switch.

'assasei 4. An electromagnetic switch having two coil portions, a source of direct current, a condenser connected to said source in series with said coil portions, and means for'connecting one of said coil portions to said source through a circuit bypassing said condenser and the other of said coil portions to cause the operation of said switch by said one coil portion after a delay due to the magnetizing force exerted by said other coil portion by the discharge of the condenser therethrough being in opposition to the magnetizing force exerted by said one coil portion.

5. ,An electromagnetic switch having two coil portions, 9. source of direct current, a condenserconnected to said source so as to be in a charged state when the switch is not operated, means for connecting to, said source one of said coil por- A tions to cause magnetizing force to be exerted by said coil portion 'suiiicient to operate said switch and for at the same time connecting said condenser across the other of said coil portions to cause through the discharge of said condenser coil portion inopposition' to the magnetizing force exerted by said one coil portion to delay the opermagnetizing force to be exerted by said other ation of the switch, and a variable resistance in series with said one coil portion for adjusting the time delay'oi said switch.

6. An electromagnetic switch having a coil, a source of direct current, a condenser connected to said source in series with-said coil, and means for connecting a portion of said coil to said source through a circuit by-passing said condenser to cause said coil portion to exert magnetizing force sufflcient to operate said switch, said by-pass circuit providing a discharge path for said condenser through the remainder of said coil to cause said coil remainder to exert magnetizing iorce in opposition to the magnetizing force exerted by said portion of said coil to delay the operation of the switch until the opposing magnetizlng force decreases due to the discharge of the condenser to a point where the net magnetizing force is sumcient to operate the switch.

7. An electromagnetic switch having a coil, a

sumcient to delay the operation of the switch until the condenser discharges to a certain voltage.

8. An electromagnetic switch having a coil, 9. source of direct current, a condenser connected to said source in series with said coil, means for connecting a portion of said coil to' said source through a circuitby-passing said condenser to cause said coil portion to exert magnetizing force suiiicient to operate said switch, said by-pass circuit providing a discharge pathfor saidcondenser into the remainder of said coil to cause said coil remainder to exert a magnetizing force in opposition to the magnetizing force exerted by said portion of said coil sufficient to delay the operation of the switch until the condenser discharges to a certain voltage, and means for shunting said coil to cause the dropping out of said switch and the quick recharge of the-condenser.

9. An electromagnetic switch having a coil, as

source of direct current, a condenser connected in series with said coil to said source so as to be charged to the voltage of said-source, and means for closing a circuit which connects a portion or said coil to said source, said coil portion when so connected exerting sufilcient magnetizing force to operate said switch, and which also connects said condenser across the remainder of said coil to cause said coil remainder to exert magnetizing force in, opposition to that of said coil portion to delay the operation oi'said switch. I

. ARTHUR WILLARD PAULSON.

WILLIAM HENRY BRUNS.

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