AU612195B2 - Method and apparatus for protecting a pump motor - Google Patents

Description

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FOR OFFICE USE Form Class: Int. Cl: Application Number: Lodged: Ob qe 0* we

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o Complete Specification-Lodged: Accepted: Published; Priority: Related Art: Name of App

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0 1 1 1 1 /Se TO BE COMPLETED BY APPLICANT licant: DEGA RESEARCH PTY.LTD a Victorian Company pplicant: 15 Century Drive, Braeside, Victoria, 3195 tor: DESMOND JOHN BERRY Address of A Actual Invent .00500 Address for Service: JOHN L.DAVIES CO. Patent Attorney P.O.Box 436 39 Cheviot Rd.) Mt.Waverley, Vic. 3149 Complete Specification for the invention entitled METHOD AND APPARATUS FOR PROTECTING A PUMP MOTOR The following statement Is a full description of this invention, including the best method of performing It known to me:-* *Note: The description Is to be typed In double spacing, pica type face, In an area not exceeding 250 mm In depth and 160 mm In width, on tough white paper of good quality and It Is to be Inserted Inside this form.

11710/78-L C I T,',uMon. Commofwe.iih ffvernmoti Prinie. Canbetrta 1 his form must be accompanied by either a provisional specification (Form 9 and true copy) or by a complete specification (Form 10 and true copy).

This invention relates generally to electronic current sensing and cut-out devices and more particularly relates to electronic surveillance for monitoring operating current conditions in an electric motor of a watercirculating and heating pump to detect an operating fault condition and switch off the pump motor.

Prior apparatus used for detecting watercirculating pump motor fault conditions such as a locked rotor condition and fur shutting down the motor comprise electromechanical devices such as a bimetallic strip cutout device sensitive to excess current flow in a locked rotor condition such as a device suff"rs the disadvantage of a long time delay taking 90 seconds operate when a motor damaging fault occurs and does not interconnect with 5 other heating equipment fitted to a spa bath, or a spa pool.

Futhermore, in commonly used prior devices a flow switch and pressure switch are mechanical devices subject to wear and breakdown and requiring a physical "break" In the hydraulic circuit which is an additional "break" location prone to leakage. Another problem is that it is necessary with prior devices to run a detection wire to this "break" point. Water-level sensing has to be fitted to the spa bath and requires wiring from a position at the water level back to a controller. There are elettiical isolation problems inherent with electrically conductive wiring back and forward between water and electrical equipment.

It is an object of this invention to provide apparatus for protecting an electric water pump motor by monitoring the motor operating current and shutting down the motor when a fault condition is detected.

The invention, according to one broad concept therefore resides in apparatus for electronically protecting an electric motor of a water-circulating pump and a heater in a closed system of a :pa pool and spa bath, the apparatus comprising operating and control circuitry for remote and automatic switching of the electric motor of the pump and for shutting down the pump; operating and j terperature control circuitry for operating a heater -2bfnatreof DOac#aa) (IMPCTANT Cross out inapplicable words in the above Form.) I 4 element of the heater and for automatically switching off the heater; fault detection circuitry for detecting a a fault of: a) abnormally high pump motor current under conditions of locked pump rotor, b) abnormally low pump motor current under conditions of low water level or no water in the pump, c) thermal deviation from a calibrated temperature range due to excessively high water temperature, d) a thermal sensor component and e) a user adjustable potentiometer.

Preferably, the thermal deviation and thermal S'sensor component fault detecting circuitry includes shortcircuit protection and high limit cut-out components.

Preferably, the fault detection circuitry includes a shut-down circuitry comprising as main operational components, two transistors, a capacitor, a fixed resistor and a first integrated circuit for open-circuit protection, the operative sequence being such that at initial power up, the capacitor is adapted to pull low, the base of one of the transistors being to first transistor to provide power supply to the circuit and to generate a signal which energizes fault condition.

S S I 1u- n jk V InwIAI .II&I '004 au -M, A practical arrangement of a preferred embodiment of the invention will now be described by way of example with reference to the components parts list following the brief description of the drawings annexed hereto in which: Figure 1 is a block diagram illustrating protection and control sub-circuits for use in a pump and heater hot water circulating system for a spa bath or pool.

Figure 2 is a schematic circuit diagram of a fault detection, temperature sensing, short circuit protection and high limit, cut-out, sub-circuit.

Figure 3 is a schematic circuit diagram of a post-fault, detection, shut-down, disabled condition sub-circuit.

Figure 4 is a schematic diagram of modified Wheatstone Bridge resistor arms sensor circuit components of Fig. 2 For establishing voltage potential, Figure 5 is a schematic diagram of a modified 02:0 Wheatstone Bridge resistor arms sensor sub-circuit, including curent sensor components of the sub-circuit of Figure 2 for establishing voltage potential.

.Figure 6 is a diagram of pump motor current .**seiising sub-circuit.

Figure 7 is a complete schematic circuit diagram including all sub-circuits 2 to 6 and all electrical and electronic components of the electrical pump motor and heater protection apparatus constructed, arranged and adapted to operate in accordance with the present invention, Referring to the drawings and to the block diagrams of Figures 1 and 7 irn particular, there is shown schematically apparatus for protecting an electric motor and/or heater of a hot water circulating pump, particularly adapted for use with a spa bath or spa pool and which comprises a complete circuit and a plurality of operationally, inter-related) separate -4-

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function sub-circuits or components, the complete circuit essentially being divided into four separate sub-circuit parts namely: fault-detection and control circuit of Figure 2, fault circuit of Figure 3, and a null-type, resistance-measuring circuit or modified Wheatstone Bridge and sensor circuit of Figures 4 and and pump motor current sensing circuit of Figure 6.

The arrangements of sub-circuit components with which the present invention is primnarily concerned are those illustrated in Figures 2 to 6 respectively, Figure 2 (referring also to the middle part of the block diagram of Figure 1) comprising a temperature sensing, short circuit protection and high curent limit detection device including components which are electronically and electrically, operationally equivalent to a classical *0 Wheatstone Bridge balancing circuit, but which is modified with one side composed of a resistor divider comprising four resistors R 1 k 2

R

3

R

4 in series as a resistance, the other side comprising fixed protective resistances R5, R6and variable resistances R7, R8, acting as a potentiometer enabling set points to be set for flucuations in temperature and user potential adjustment, functioning as a potentiometer allowing voltage selection for short circ''.t protection and high 5 limit cut out.

Referring to Figure 3, the fault shut-down S circuit essentially comprises as main operational components, two transistors T 2 and T 3 capacitor C 4 and fixed resistor R17 and at initial power up the 3* capacitor C 4 pulls the base of transistor low, S* providing power supply to the circuit. The signal energises the fault detect and control circuitry and if no fault level is present, output of pins 1, 2 on integrated circuit IC1 is high which drives through 1 fixed resistor R 17 to hold the transistor Tg on supplying base drive for transistor T 2 When a fault is detected, the pins 1, 2 of IC1 fall turning off T 1 3 1 i. L- I -Ii I which turns off T disconnecting power to the main 2 circuit, which in turn, turns off supply to the relay.

Referring to Figure 4, the sub circuit type arrangement of resistors shows a set arm and Figure shows a detect arm with sensor and set point control these components forming part of the circuit of Figure 2. Output of IC13 controls the heater relay and when high, the relay is on, the low heater relay is off.

R

11

R

12 are feedback resistors to set hysterises transistor T 1 and capacitor C3 resistor R9 and diode

D

1 set up a time delay which inhibits the heater output for a set time delay (which is determined by C3,

R

9 D 17 R 10 until stable flow conditions are reached in the hydraulic circuit ICi together with the resistor arm of Figure 4, sets up a high limit fault detect circuit which trips the fault shut-down circuit, when the sensed temperature is a controlled amount above the set temperature. The temperature of the high limit shutdown is set by R 2 and resistor values in both arms .20 of the Wheatstone Bridge IC13 provides fault detection to prevent occurence of a short circuit of sensor probe wires which may be run to a remote location and are .o susceptible to short circuit and open circuit (IC1 protects against open circuit). Electric pump motor fault detection is achieved ICI4, where a current transformer coil AC output current is rectified, smoothed and applied to adjustable resistance potentiometer RV 2 2 This circuit provides a voltage which is proportional to the electric motor current d the adjustment of the motor shut down level to be Smade. ICl 4 compares current sense circuit voltage against a fixed reference voltage set by D 1

T

1 and when the motor current falls, voltage across RV 22 falls and the output of ICI 4 becomes low tripping the fault shutdown circuit of Figure 3.

-6- Advantages of the invention are that the necessity of wiring at the source of faults is eliminated and a locked motor, rotor current sensing device is provided which senses a default condition in approximately 10 seconds and then immediately switches off power to the electric motor and other equipment, such as heater and when once a fault is detected, the system of the invention remains in the "off" state.

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Claims (6)

1. Apparatus for electronically protecting an electric motor of a water circulating pump and a heater in a closed system of a spa pool and spa bath, the apparatus comprising operating and contrcl circuitry for remote and automatic switching of the electric motor of the pump and for shutting down the pump; operating and temperature control circuitry for operating a heater element of the heater and for auto- matically switching off the heater; Fault detection circuitry for detecting a fault of: a) abnormally high pump motor current under conditions of locked pump rotor, b) abnormally low pump motor current under conditions of low water levelor no water in the pump, c) thermal deviation from a calibrated temperature range due to excessively high water temperature d) a thermal sensor component and ee) a user adjustable potentiometer.

2. Apparatus according to claim I, wherein the thermal deviation and thermal sensor component fault detecting circuitry includes short-circuit protection and high limit eve* cut-out components.

3. Apparatus according to claim 1 or 2, wherein the fault detection circuitry includes a shut-down circuitry comprising as main operational components, two transistors, a capacitor, a fixed resistor and a first integrated circuit for open-circuit protection, the operative sequence being such that initial power up, the capacitor is adapted to pull low the base of one of the transistors being to first transistor to provide a power supply to the circuit and to generate a signal which energizes fault condition.

4-'l RAO /I-8- 0 t) W~'rO detection and control circu4,try and if no fault level of current is present, output of pins on the integrated circuit is high thereby driving through the fixed resistor to maintain the second s9aid transistor or supplying a base drive for the first said transistor whereby when a fault condition is detected, the output pins of the integrated circuit fall switching off said second transistor which switches off the said first transistor disconnecting power to the main circuit and in turn switching off electrical supply to a relay. -6f Apparatus according to claim 2 wherein the fault detection and control circuit includes a modified Wheatstone Bridge with a setting arm and a detection arm with sensor and set point control, an se* 0*00 integrated circuit for controlling the output of n :~.heater relay whereby, when the value is high, the *see relay is activated, the low heater relay is de- activated, two feed-back resistors setting a hysteris t-ansistor, a capacitor, a third resistor and a diode to create a time delay for inhibiting the heater output for a set time delay, until stable water flow conditions are reached within a hydraulic, water-flow circuit, the integrated circuit together with the Wheatstone Bridge resistor arm forms a high limit, fault detection, electric circuit for tripping the fault shut-down circuit, when the sensed temperature is a controlled amount above the set temperature and resistor values in both arms of the Wheatstone Bridge. 6 I Apparatus according to any one of claims 2 to wherein a third integrated ciercuit is provided for fault detection to prevent occurrence of short circuit of sensor probe wires which may be run to a remote location and which are suspectible to short circuit.

9- i ir CP I. Apparatus according to any preceding claim wherein electric pump motor fault detection is b'7 achieved incorporation of a fourth integrated circuit equal in rating to the first, second or third integ- rated circuits wherein coupling of a current transformer coil AC output current is rectified, smoothed and applied to an adjustable resistance potentiometer in a circuit providing voltage proportional to a pump electric motor current and adjustment of motor current shut down level. Apparatus according to claim 7 wherein the fourth integrated circuit is a current sense comparator for circuit voltage against a fixed reference voltage set by a first diode and a first transistor, whereby ego when the pump motor current falls, voltage across the adjustable resistance potentometer falls and the output of the fourth integrated circuit becomes low, tripping *0 the fault shut-down circuit. S. 9. A me 'd for prou ec i'ng an- ulec -t ic muora of- water circulating pump, which method comprises electronically, automatically sensing abnormal perating current levels in the windings of the sai electric pump motor comparing the motor winding cup t with a calibrated set point and automa j-cally shutting down the 4* motor and heater, when thee 5is detected an abnormal current deviation co saponding to a fault condition top* such as a pump being filled with water, or having a dischar side blockage, the motor and heater remai ng switched off while the default condition ev, ails i-. L Apparatus for electronically protecting an electric motor (and/or heater, where fitted) of a water circulating pump substantially as hereinbefore described with reference to Figures 1 and 7 of the accompanying drawings. I 1h. Apparatus for electrically protecting an electric motor (and/or heater, where fitted) of a water circulation pump and comprising fault detection and shutdown circuit substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings. Apparatus for electronically protecting an electric motor (and/or heater, where fitted) of a water circulation pump and comprising a fault sensor circuit substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

13. A method for protecting an electric motor of- a water circulating pump, which method comprises-fasuring the "slip" and/or the rotating speed of sajid~"motor to determine motor load conditions by measurement of motor I0"* current phase and direct comparltive measurement of the V ae speed of rotation of said _Jifor with frequency of the AC current wave formof the motor. S* 14. A metl or methods for protecting an electric motor of -ater circulating pump substantially as here efore described and or illustrated. *w S* DATED this 9th clay of November 1988 4 DEGA RESEARCH PROPRIETARY LIMITED S, By their Patent Attorney: JOHN L. DAVIES CO. -11- i i