Abstract: Embodiments are directed toward a spike strip. The spike strip preferably includes a housing, a plurality of spikes disposed in the housing, a door, and a mover. The door is preferably configured to transition between a closed configuration in which the spikes are covered and prevented from puncturing tires of vehicles driving over the spike strip and an open configuration in which the spikes are exposed and allowed to puncture a tire of a vehicle driving over the spike strip. The mover is preferably configured to transition the door from the closed configuration to the open configuration responsive to a signal provided to the spike strip from a remote location.

Abstract: A braking system can include a monitor circuit and/or a contactor control circuit. The braking system utilizes a number of contactors coupled between a power bus. The contactors selectively provide power to resistive elements. The monitor circuit is configured to determine the number of closed contactors of the contactors using current transformers. The contactor control circuit is configured to open and close the contactors. The control circuit includes a solid state timer circuit for each coil associated with the contactors. The solid state timer circuit bypasses a resistive element in series with the coil for a period of time.

Abstract: A first timing comparator TCP1 latches a data signal at a timing that corresponds to each edge of a first strobe signal. A first delay element delays a first strobe signal so as to output a first delayed strobe signal. A first clock recovery unit makes a comparison between the phase of the first delayed strobe signal and a clock signal, and outputs a first reference strobe signal which is used to perform phase adjustment such that the phases of these signals match each other. A third delay element delays a first reference strobe signal, and outputs the signal thus delayed as the first strobe signal. A delay amount that corresponds to the amount of skew that occurs between the data signal and the clock signal is set for the third delay element.

Abstract: A method and apparatus measures electrical power usage and quality, while mitigating the effects of noise on measured signals or parameters. Specifically, a digital electrical power and energy meter employs a method in which a processor averages a parameter, such as voltage or current, over a plurality of cycles of a time-varying signal, such as an AC electrical signal. The method employed by the meter samples a parameter over the plurality of cycles and computes the average of the samples corresponding to the same phase angle of the signal to produce an average signal.

Abstract: An audio reproducing apparatus includes a power supply, an amplifier, a speaker, and a controller. The power supply is for supplying a voltage. The amplifier is for receiving the voltage and audio signals, amplifying the audio signals, and outputting amplified audio signals. The speaker is for reproducing sound after receiving the amplified audio signals. The controller is for receiving the voltage and generating a control signal to enable the amplifier. The controller includes a generator and a delay unit. The generator is for receiving the voltage and generating the control signal. The delay unit is for delaying the time of transferring the voltage from the power supply to the generator.

Abstract: A method and apparatus measures electrical power usage and quality, while mitigating the effects of noise on measured signals or parameters. Specifically, a digital electrical power and energy meter employs a method in which a processor averages a parameter, such as voltage or current, over a plurality of cycles of a time-varying signal, such as an AC electrical signal. The method employed by the meter samples a parameter over the plurality of cycles and computes the average of the samples corresponding to the same phase angle of the signal to produce an average signal.

Abstract: The present disclosure describes a new pushbutton incorporated into new circuit configurations of an improved intelligent electronic device (“IED”), for use in power substation control systems. The new pushbutton is non-mechanical and configured to control a breaker, or other type of substation equipment, after an IED associated with the circuit breaker, or other type of substation equipment, fails to operate. In an embodiment, the new pushbutton may be a low-energy, membrane-type pushbutton. During normal operation, a microprocessor within the IED operates a solid-state device to control the operation of substation equipment. When the IED fails, manually depressing the new pushbutton bypasses the IED microprocessor and manually controls the substation equipment associated with the failed IED.

Abstract: A circuit and related methods for use in a hybrid power switching device are provided that include at least one electromechanical relay having a coil and a contact, the electromechanical relay defining a release time and a sticking time during an on-to-off transition. At least one solid state switch is electrically connected to the contact, and a timing circuit is electrically connected to the electromechanical relay and the solid state switch. The timing circuit includes a capacitor electrically connected to a control signal input and at least one resistor electrically connected to the capacitor and to the solid state switch, wherein the capacitor and the resistor are sized such that the capacitor discharges through the resistor to activate the solid state switch for a period of time that is longer than the electromechanical relay release time and sticking time.

Abstract: A method and apparatus for remotely operating a circuit protection device, such as a circuit breaker, to move the circuit protection device to an open condition to disconnect a load from a power source. The apparatus includes a control circuit positioned externally from the circuit protection device. The control circuit includes an impedance limiter and a switching device connected in series with each other. The impedance limiter and switching device are positioned in parallel with the load. The switching device can be remotely actuated to move between an open position and a closed position. When the switching device is in the closed position, the impedance limiter draws a supply of current through the impedance limiter. The size of the impedance limiter is selected such that the current drawn from the power source is greater than the trip current required to move the circuit protection device to the open position. Thus, the switching device can be used to remotely actuate the circuit protection device.

Abstract: An electrical control module and circuit for controlling a solenoid. The control circuit provides a constant voltage to a solenoid for a predetermined time period after which a pulse width modulated voltage is supplied. The circuit further includes components for reverse polarity protection, transient voltage protection, low gate drive voltage protection, reduced heat dissipation and improved magnetic drive under low input voltage conditions during application of the pulse width modulated voltage. The module may be used in conjunction with a single coil or a dual coil solenoid. The circuit may be utilized on a 12 volt or a 24 volt electrical system without adjustment.

Abstract: A hybrid relay with an electromagnetic relay system having at least one coil one core yoke unit, at least one armature which switches contacts and one power semiconductor whose switching path, in combination with the contacts switches the load circuit of the relay wherein the contacts are switched on no-load by offsetting the control of the power semiconductor in time resulting in good heat dissipation and a compact design with few individual parts.

Abstract: In an input protection circuit, a bipolar protection device is constituted of a semiconductor substrate of a first conductivity type, a first diffused layer of a second conductivity type formed in the substrate and connected to an input signal pad, a second diffused layer of the second conductivity type formed in the substrate to extend in parallel to the first diffused layer but separately from the first diffused layer by a first space, and a third diffused layer of a high impurity concentration and of the first conductivity type formed in the first space in the substrate to extend in parallel to the first and second diffused layers, in junction with the second diffused layer but separately from the first diffused layer. When a backward biasing voltage is applied, the thickness of a depletion layer formed is made large, so that generation of hot carriers is minimized.

Abstract: A remote closing operator is positioned within a circuit breaker enclosure to allow remote operation of the circuit breaker operating mechanism to close the circuit breaker contacts. A closing solenoid and associated logic circuit controls the state of the contact closing springs. The solenoid is energized to initially release the contact closing springs and is later prevented from operation upon any further attempt to release the contact closing springs after the contacts are closed.

Abstract: An electronically controlled latching circuit breaker capable of being remotely set or tripped. The electronic controls are current sensitive rather than thermally activated.

Abstract: This invention is directed to an improved PCMCIA frame kit for receiving a planar electronic device, such as a printed circuit board or memory card, for electrical engagement with a complementary device in electronic equipment, such as a computer. The kit comprises a pair of matable, cover members to provide shielding to the planar electronic device, and that each cover member is integrally molded to a dielectric frame upon which the planar electronic device is seated. The improvement hereof lies in the provision of each frame including a dielectric extension intermatable with one another to define a cavity for receiving a portion of the planar electronic device. By this arrangement the planar electronic device may be provided with an antenna for the transmission of signals through the dielectric extension. Optionally, the cover members and extensions may be essentially identical in construction having appropriate means about the periphery thereof, for intermatability.

Abstract: A contactor control system for a DC electric power system for reducing contactor tip contamination from dry-switching includes a first switch connected in circuit between a power source and a controller for enabling the controller upon closure of the first switch. A PTC resistor is connected between the first switch and a filter capacitor whereby charging current is supplied to the capacitor upon closure of the first switch. A solid-state switch is connected in series circuit with an electromagnetic actuator of a contactor having power contact tips in circuit between the power source and a load. The series combination of the actuator and solid-state switch is connected in parallel circuit with the filter capacitor.

Abstract: A relay control circuit in which a capacitor is used as a power source of a transistor which prohibits operation of the transistor which is operated by input by switch operation. If power is no longer supplied to the entire relay control circuit while the capacitor is discharging, switch input is prohibited.

Abstract: In a vehicle electromagnetic clutch control device, clutch current calculating means outputs a clutch current analog signal according to given travel control data and engine control data, a current difference detector obtains the difference between the clutch current analog signal and a clutch current feedback signal, a first output transistor is operated according to the difference thus obtained to energize the electromagnetic clutch, the clutch current flowing in a second output transistor is detected with a current detecting resistor, and a voltage corresponding to the clutch current thus detected is applied to an operational amplifier, so as to output the clutch current feedback signal with the aid of a reference resistor, a feedback resistor and the amplification factor thereof. An adjusting resistor is connected in parallel to the reference resistor, to adjust the clutch current.

Abstract: An interface to facilitate storing in an electric utility meter transponder, water usage data so that when remotely interrogated, access can be had to both electric and water usage data. A pulse indicative of water usage sets a magnetic latching relay in the interface circuit which causes a transponder supply voltage to be switched to two interface circuit timers. The first timer generates a first delay, after which the electric meter transponder is pulsed to register water usage. After a second, longer delay, the second timer resets the magnetic latching relay to thereby place the interface circuit in condition for receiving another water usage signal.

Abstract: A trigger circuit for an electromagnetic device, in particular a solenoid valve of an injection system for an internal-combustion engine, has a control element for causing excitation of the electromagnetic device to be lowered at least once and then raised after the electromagnetic device is activated. The control element has a delay circuit which slows down the rate at which excitation of the electromagnetic device changes during the lowering and/or raising action.

Abstract: A timed contact switch apparatus has a conventional pushbutton placing a main switch in an actuated state when the pushbutton is depressed. A timing circuit is activated by the pushbutton to provide power to activate an electromechanical latch which holds the main switch in its actuated state while the timing circuit times out. Preferably the timing circuit operation is initiated by output of a Hall sensor which is controlled by a magnet whose position is mechanically linked to the position of the pushbutton.

Abstract: Solid state control circuitry for driving an electromagnetic armature of a battery operated electric stapler. The armature is activated by a trigger signal generated by a trigger switch which discharges an energy storage device through the armature. Energy is rapidly replenished in the energy storage device following its discharge; but if a subsequent trigger signal is not forthcoming, the control circuit reverts to a quiescent state, thereby reducing power consumption.

Abstract: A safety control device for an actuator of a flap solenoid valve, such as for an automatic transmission. The device includes a current control device which is connected to a shunt resistor for measuring the current through the solenoid valve and the current control device. It also includes a control package which measures the time between the starting of the power to the solenoid valve and the moment when the current reaches a threshold intensity. The control package compares this time with a time range which indicates the proper operation of the solenoid valve so that if the time falls outside this time range, the control package instructs the current control device to cut power to the solenoid valve.

Abstract: A low pressure metering pump having a hollow piston reciprocated in a cylindrical guide by a solenoid coil. A pair of check valves provide for unidirectional fluid flow through the cylindrical guide in response to the reciprocation of the piston. A seal attached to the piston prohibits a fluid backflow between the external surface of the piston and the internal surface of the cylindrical guide. A bumper seal at the output end of the piston prevents fluid flow through the cylindrical guide when the solenoid coil is de-energized. A control circuit periodically energizes the solenoid coil at a frequency determined by a variable resistance responsive to predetermined operational parameters. In a preferred embodiment, the metering pump is a fuel control element for a heater and the variable resistance is a thermistor or similar type of temperature sensitive resistance, which controls the rate at which fuel is delivered to the heater.

Abstract: A low pressure metering pump having a hollow piston reciprocated in a cylindrical guide by a solenoid coil. A pair of check valves provide for unidirectional fluid flow through the cylindrical guide in response to the reciprocation of the piston. A seal attached to the piston prohibits a fluid backflow between the external surface of the piston and the internal surface of the cylindrical guide. A bumper seal at the output end of the piston prevents fluid flow through the cylindrical guide when the solenoid coil is de-energized. A control circuit periodically energizes the solenoid coil at a frequency determined by a variable resistance responsive to predetermined operational parameters. In a preferred embodiment, the metering pump is a fuel control element for a heater and the variable resistance is a thermistor or similar type of temperature sensitive resistance, which controls the rate at which fuel is delivered to the heater.

Abstract: A forced air gas heating furnace system includes a thermostat having a transformer for converting the typical household 115Vac to a 24V thermostat ac control voltage, and a switch, the thermostat elements connected to the junction of an ac to dc converter, a digital control circuit and a TRIAC. The dc output is connected to a dc voltage regulator which outputs Vcc for a digital control circuit. The gate of the TRIAC is connected to the output of the digital control circuit, and operates in response thereto for selectively triggering the TRIAC for passing the 24Vac transformer control power to a solenoid operated gas valve.

Abstract: Method and apparatus for controlling and operating the return ball lift mechanism in a bowling alley. In a preferred embodiment the motor which drives the lifting belt is normally inoperative and it is actuated when a ball arrives to be lifted into the storage rack. A photo detector is utilized to detect the presence of the returning ball and provision is made to actuate the motor for a total of four seconds. In the event a second ball arrives before the end of four seconds, timing begins all over again. A feature of the invention is the elimination of a centrifugally operated switch to control the START winding of the motor as a solid state timer controls the operation of both windings of the motor.

Abstract: An improved duty cycle timer provides a duty cycle control signal having alternate "on" and "off" intervals of different logic states. The timer utilizes integrated circuitry having first and second independent clock sources respectively driving first and second multistage, binary counters. One counter measures the "off" interval and the other counter measures the "on" interval. Each counter provides a signal representative of the completion of the interval which it measures, and that signal is connected to a resetting input of the opposite counter for initiating the measuring interval of that opposite counter. Typically, one interval is longer than the other. The duty cycle control signal is provided by the output of one of the counters. In an illustrated embodiment, the duty cycle timer controls operation of a defrost mechanism for a refrigeration circuit and the "off" interval is longer than the "on" interval.

Abstract: A machine tool timing relay has immunity from electrical noise on a control signal, and has an oscillator capable of generating pulses having a predetermined frequency, a means for adjusting the predetermined frequency over a continuous range of frequencies, a counter capable of counting the pulses and capable of generating an output signal after a predetermined number of the pulses are counted, means responsive to a start signal for initiating the counter to count the pulses, an optical isolator circuit responsive to the control signal for generating a light, detecting the light, and generating the start signal in response to detecting the light in order to isolate the counter from electrical noise mixed with the control signal, an electrical contact, and an output circuit responsive to the output signal for operating the electrical contact when the counter generates the output signal so that the contact is operated after the counter counts a predetermined number of the pulses.

Abstract: A moisture sensor having an oscillator circuit with its output frequency directly proportional to moisture percentage present in the substance of interest, such as soil. The oscillator circuit includes two spaced plates in the substance which function as a capacitor. The frequency of the oscillations changes as the capacitance between the plates changes due to the moisture present between the plates. The sensor is particularly adapted for use as a soil moisture detector and provides indications of moisture percentage or end points such as wet or dry conditions.

Abstract: A moisture sensor having an oscillator circuit with its output frequency directly proportional to moisture percentage present in the substance of interest. The oscillator circuit includes two spaced plates in the substance and functioning as a capacitor. The frequency of the oscillations changes as the capacitance between the plates changes due to the moisture present between the plates. The sensor is particularly adapted for use as a soil moisture detector and provides indications of wet or dry conditions.

Abstract: The control circuit for use with an electromagnetic coupling apparatus comprises a timer started when a power source switch is closed, an oscillator started by the switch and stopped by the timer, and a drive circuit which intermittently passes current through an exciting coil of the electromagnetic coupling apparatus in accordance with the oscillation output of the oscillator and continuously passes current through the exciting coil when the oscillation output is stopped.

Abstract: A circuit for controlling a solenoid clutch wherein a gap is present between an electromagnet and an associated attracted member when in the disengaged state. The circuit controls the level of exciting current supplied to an exciting coil of the solenoid clutch in such a way that the width of the gap is first reduced to zero and then the slip rate of the solenoid clutch is gradually changed from 1 to 0, whereby the solenoid clutch gradually reaches the completely engaged state, making it possible to smoothly engage the solenoid clutch without the occurrence of mechanical shock.

Abstract: The invention relates to a circuit arrangement for actuating exciting coils for electromagnetic switchgear. A transistor is connected in series with the exciting coil, as an electronic switch. Parallel with the series connection are a capacitor and a clock generator, which opens and closes the transistor with a certain frequency. Thereby, upon opening, a defined turn-off delay of the electromagnetic switchgear, and upon switching on, with the use of a timing element which at first deactivates the clock generator, the effect of a d-c saver circuit for electromagnetic switchgear can be achieved.

Abstract: A delay circuit 2 utilizes two comparator timers 4 and 6 and a minimum of logic to achieve a combination ON/OFF delayed function. The comparator timers 4 and 6 are resettable independently of each other such that each respective ON or OFF delay function may begin retiming without waiting for the other delay function to time out if the input signal transitions back and forth before the end of the respective ON or OFF delay. The delayed circuit 2 is ideal for proximity switch applications, particularly photoelectric type proximity switches, for providing a delayed output signal following a given sensed condition.

Abstract: A one-shot delay timer 4 is provided by a pair of comparator timers 14 and 18. The first comparator timer 14 responds to an input signal and provides a delayed output initiating the output pulse. The second comparator timer 18 provides a delayed output terminating the output pulse. The delayed output pulse of controlled length is generated for each input signal except when a second input signal occurs before the termination of the one-shot output pulse. The delayed output pulse is generated regardless of the duration of the input signal, even if the input signal lasts longer than the termination of the output pulse. Timer 4 is ideal for proximity switch applications, particularly photoelectric type proximity switches, for providing a delayed output signal following a given sensed condition.

Abstract: A timer circuit suitable for operating, for a required period of time, the windshield defrosting heater in an automobile, comprises a switch operative only in one direction, such as a momentary unidirection switch, a timer which starts timing operation after a lapse of a predetermined time, and a flip-flop circuit or the like. The switch allows setting and cancelling for timing operation, whereby the operative characteristics are improved and the mechanical design is simplified. Moreover, the use of a flip-flop circuit reduces the occurrence of chattering.

Abstract: An electrical circuit, the starting circuit for a motor vehicle for example, is selectively enabled by a control circuit which includes a magnetic field responsive switching device. Proper positioning of a magnet which provides a field of the appropriate polarity and strength relative to the switching device results in the energization of a relay which has contacts connected in series with the circuit being controlled. In the motor vehicle application, operation of the ignition switch within a pre-determined time subsequent to removal of the magnet will latch the relay in the energized state.

Abstract: An improved power switch circuit for turning on manually and for turning off either manually or automatically a battery operated electronic instrument. The circuit includes one manual momentary contact on/off switch, a bilateral switch or transmission gate, a microprocessor, and a capacitor that charges to a threshold level when the on/off switch is momentarily closed (on) and that discharges when either the on/off switch is momentarily closed again (off) or after a fixed amount of time has elapsed as determined by the microprocessor. The bilateral switch is switched on when the threshold potential is reached thereby preconditioning the on/off switch for turning the instrument off. The on/off switch can now be closed to discharge the capacitor or the microprocessor can discharge the capacitor thereby switching off the bilateral switch and preconditioning the on/off switch for again turning on the power to the electronic instrument.

Abstract: A start circuit arrangement for a microwave oven including a power control relay circuit which is independently responsive to a user actuable momentary start switch and to a programmed electronic controller to facilitate operation in a delay start mode. The relay circuit includes a start latch circuit, a door switch and an arm switch. User actuation of the momentary start switch sets the latch circuit. A signal from the electronic controller resets the latch circuit. The door switch is closed by closure of the oven door. The arm switch is closed by an arm signal from the electronic controller when an actual cooking cycle is to begin. The arm signal is removed upon expiration of the cooking cycle. The arm switch, start latch means and door switch are all operatively coupled to the relay such that the relay only enables energization of the power circuit for the oven when the arm switch and door switch are closed and the start latch is set.

Abstract: A control circuit arrangement for an electromagnetically operated power tool has a primary circuit including a solenoid and a semi-conductor switch, in series, the semi-conductor switch being capable of being triggered into a conducting state upon application of a trigger signal from a trigger control circuit. The trigger control circuit is actuated upon closure of a main trigger switch which is connected in series with the solenoid and the semi-conductor switch in the primary circuit for supplying current to the solenoid. Thus, should the semi-conductor switch fail due to a short-circuit, the power supply is disconnected from the solenoid the moment the operator releases the main trigger switch so protecting the solenoid. The semi-conductor switch is preferably a thyristor. An additional circuit is preferably provided for preventing the thyristor from firing a second time if the main switch remains closed.

Abstract: A testable load driving circuit apparatus includes a solid-state load driver for controlling AC current loads coupled in series with a winding of a saturable core reactor used for sensing the presence or absence of load current through a load current monitor which is coupled to another winding in the reactor. The load driving circuitry may be tested during circuit operation by injecting a signal of insufficient duration to substantially affect the load circuit.

Abstract: With this circuit, a current may be caused to flow through a contact (K) controlling the voltage supply of an electronic control circuit (24), of sufficient intensity for the reliability of the contact to be good, without the current flowing in the control circuit (24) being too high and this independently of the supply voltage (terminals E, 44) applied to the supply terminals of the user circuit (U). For this, the control circuit (24) is fed with power when the contact (K) is closed, through said contact (K), a first diode (31) and a resistor (32) connected in series, whereas a piloting circuit (11), which is an integrated time delay or memory circuit associated with said user circuit (U), is then supplied through said contact (K) and a second diode (26). When contact (K) is open, said piloting circuit (11) is fed through a third diode (29) and a Zener diode (30), the second diode (26) then preventing the control circuit (24) from being supplied with power.

Abstract: A battery control and alarm system for a vehicle electrical system including a first, normally open, solenoid-actuated switch connected in series with the main battery cable; a second, magnetically actuated reed switch proximate the vehicle ignition switch and connected to the battery; and circuitry to close the first switch when the second switch is closed and for a limited delay period after the second switch is opened. In a preferred embodiment, the system includes a third, magnetically actuated reed switch and circuitry to both sound the vehicle horn and close the first switch when the third switch is closed.

Abstract: A circuit for providing an adjustable period of delay in a vehicle which is started by engaging the engine of the vehicle and a brake means, then disengaging the brake means after the period of delay, has a relay for selectively engaging and disengaging the brake. A variable time delay provides the period of delay. A switch selectively causes the relay to engage the brake and then to disengage the brake after the period of delay. A safety activation means prevents the relay from engaging the brake means in the absence of the switch selected to cause the relay to engage the brake means.

Abstract: An electronic control circuit for the formation of a monostable switching behavior in a bistable relay, including a logic circuit for the conversion of binary input signals into control signals for a switching circuit through which the direction of current flow is reversible within the relay, whereby the relay is switchable at each status change of the input signal. The electronic control circuit includes at least one time pulse generating circuit with an at least single-step divider circuit, wherein the input signal is applied to an interrogating circuit through which first control signals can be generated immediately after each status change of the input signal and in synchronism with a predetermined timing pulse, and in which the switching circuit consists of a bridge circuit controlled by the first control signals, through which the relay is supplied with short power pulses whose polarity can be reversed by the control signals.

Abstract: The invention is an improved control for an air conditioner unit in an automobile. The control operates on a time cycle basis instead of using a sensor of air temperatures. The installation is simple, requiring the severing of an electrical lead in the automotive electrical system and making three electrical connections from the invention to the wiring of the automotive electrical system. The invention consists of an adjustable range control, an interval timer, and a relay driver. This combination is connected to the magnetic clutch of the air conditioning unit.

Abstract: A drive circuit for a latching relay includes a flip-flop, a timer and a semiconductive switching circuit for the relay. First and second input signals are applied to the flip-flop and first and second control signals at the output of the flip-flop are applied alternately to the timer as a time limit output for controlling the energization of the switching circuit in concert with a high-speed changeover signal.

Abstract: A relatively inexpensive electronic delay timer particularly suitable for portable use in such applications as control of a camera shutter. The timer can be used in either a leading or trailing mode and employs a small 6V battery as a power source. An integrated circuit timer device is arranged to provide an output signal at the end of a time delay period which can be variably selected by means of a built-in capacitive-resistive network and which is arranged to start in response to a movement of an external control switch. The output signal triggers a second time period of predetermined duration in a second integrated circuit timer during which time a second output signal is generated thereform which is used to activate a transistor device, allowing a capacitor in the circuit to discharge therethrough and through a solenoid which is mechanically coupled to the camera shutter. When the second output signal ceases, at the end of the second time period, the transistor is deactivated and the capacitor recharges.

Abstract: A circuit for providing an adjustable period of delay in a vehicle which is started by engaging the engine of the vehicle and a brake means, then disengaging the brake means after the period of delay, has a relay for selectively engaging and disengaging the brake. A variable time delay provides the period of delay. A switch selectively causes the relay to engage the brake and then to disengage the brake after the period of delay. A safety activation means prevents the relay from engaging the brake means in the absence of the switch selected to cause the relay to engage the brake means.