GB2086025A - A warning system indicating a compressor breakdown - Google Patents

Abstract

A bulk milk storage tank T is surrounded by a water jacket J, and associated with a refrigeration system for promoting the formation of an ice bank. Operation of the compressor C of the refrigeration system is controlled and monitored by a unit U including an audible alarm A and warning lamps L1 to L3 for indicating a compressor fault. The compressor includes low pressure fault sensors (LP, LP'), high pressure fault sensors (HP, HP') and a temperature sensor (K). <IMAGE>

Description

SPECIFICATION Improvements in bulk milk storage In modern dairy farming, milk is stored and cooled while awaiting collection in a bulk milk tank or vat having a jacket containing a quantity of water in which an ice bank is caused to form by a refrigeration unit associated with the tank. The ice bank is capable of serving as a heat sink for a certain period of time while the refrigeration unit is out of action as the result of a fault or power failure. Ideally, the ice bank is large enough to exist for at least 12 hours in order to permit a further milking to take place, and to permit the attendance of a repair person or the resumption of the power supply before the stored milk becomes unfit for consumption.

A disadvantage of the known tank is that a compressor fault may go unnoticed until after the ice bank has melted. Consequently, because regulations prohibit the collection of uncooled milk, the milk already stored in the tank is wasted as is that derived from subsequent milkings until the fault is rectified. This problem is overcome by the equipment which will now be described by way of example with reference to the drawings, in which: Figure 1 illustrates diagrammatically a bulk milk tank together with a refrigeration unit and a control, monitoring and warning system associated with the tank, and Figure 2 is a circuit diagram of a preferred form of control, monitoring and warning system.

Referring to Figure 1, the bulk milk tank is shown at T surrounded by its jacket J containing the quantity of water in which the ice bank is caused to form about piping P through which a refrigerant is circulated by means of a compressor indicated diagrammatically at C.

During normal operation, the compressor is controlled in dependence on the size of the ice bank which is sensed by an ice bank sensor IB which may be of the type including a capillary tube and a switch operated in response to the position of fluid within the tube. Typically, in a refrigeration unit of the type used with a bulk milk tank, the pressure of the refrigerant on the intake side of the compressor is normally in the range of 1 5 psi to 19 psi. A leak or other fault may cause the pressure to fall below this range for a prolonged period, with the result that ice will cease to form or will form at an insufficient rate. To provide indication of a lower pressure condition, two low pressure sensors LP and LP' are located at the intake side of the compressor. Each sensor is arranged to respond when pressure falls to a respective predetermined level.For example, sensor LP' responds when pressure falls to 10 psi and sensor LP responds at 8 psi, at which ice ceases to form at a satisfactory rate. The pressure of refrigerant at the discharge side of such a compressor is normally within the range of 95 psi and 11 5 psi, a pressure in excess of this range indicating that condensation of the refrigerant is not taking place as the result of a blocked air inlet, for example. Again the result of such a fault is to cause ice to form at an insufficient rate. A high pressure condition is sensed by two high pressure sensors HP and HP' at the discharge side of the compressor. Sensor HP' responds at 125 psi and sensor HP at 1 50 psi, for example. Both the low and high pressure sensors may be easily adjusted to respond at different pressures, depending upon operating conditions.A temperature sensor K for example of the bi-metallic strip type sold under the trade name Klixon, is arranged to respond if the temperature of the compressor exceeds a fixed value. The sensors LP, HP and K operate when the condition of the compressor is such that it should be shut-down, and are referred to as fault sensors.

Sensors LP' and HP' operate when there is a potential fault condition but without shut-down being necessary.

The compressor is operated by an electric motor supplied with electricity at mains voltage through a power circuit including a switching device operated by a control system including the fault sensors described above. The switching device is closed in order to make the power circuit and start up the compressor when the sensor IB signals the need for more ice and to break the power circuit to stop the compressor when the sensor IB signals the presence of an ice bank of sufficient size. The control system is arranged to cause the switching device to break the power circuit and stop the compressor when any of the fault sensors LP, HP and K signals a fault in the compressor.Associated with the control system is a warning system for actuating an alarm preferably of an audible and visual nature when the compressor ceases to operate as a result of a fault or power failure and a monitoring system which provides an indication of certain types of fault.

In Figure 1, a control, monitoring and warning unit U is housed within a perspex-fronted cabinet or box mounted in a convenient and conspicuous location, for example on the wall of the milking parlour. Within the cabinet is disposed the switching device S, and audible alarm A and a warning lamp L1, as well as monitoring lamps L2 to L8.

Conveniently, the sensors IB, LP and HP all include switches which, like the temperature sensor K, are closed when the compressor is to operate, whereas the sensors LP' and HP' include switches which are normally open but close in a fault condition. The control system includes a circuit in which the switches of elements IB, LP and HP are arranged in series, the control circuit including the coil of the switching device, so that the power circuit is made when the control circuit is live and the switching device coil is energised.

With this arrangement, conductors extending from the unit U to the various sensors form the control circuit, and the monitoring and warning systems may include circuits including a bank of electromechanical relays R arranged within the unit U and responding to the condition of various portions of the control circuit and the power circuit.

The control circuit preferably operates on a low voltage direct current derived from a suitable power source supplied from the mains supply and it is possible for the warning circuit to be supplied from this power supply. However, such an arrangement would not permit warning to be given of a fault in this power supply and therefore, preferably, a separate low voltage direct current power supply PS is provided for a least part of the warning circuit.

Referring now to Figure 2, the control, monitoring and warning circuits will now be described. In Figure 2, the switches of the ice bank sensor, low pressure sensors and high pressure sensors are indicated at IBS, LPS, LPS', HPS and HPS', the location of these switches and of the sensor K within broken lines indicating that they are disposed externally of the unit U. All of the remaining circuit elements are disposed within this unit. Considering the various circuits in turn: Control Circuit Within the unit U, the control circuit includes a line extending between a terminal 1 and a common neutral line 5. The terminal 1 is connected to the positive of a control power source supplying a 24 volt, direct current.Within the unit U, the line is provided with terminals for connecting by way of the conductors shown in Figure 1 with the switches IBS, LBS, HPS and sensor K so as to connect these elements in series with the coil of the switching device S of the 240 volt, alternating current, power circuit shown in heavy lines. When the compressor is in an efficient working condition, the switches LP and HP are closed and the sensor K is unbroken. Assuming that the ice bank needs to be replenished, switch IBS is closed to make the control circuit, current flowing from terminal 1 to the common neutral line 5. The coil of the switching device S is energised and the power circuit is made. In the event of a low or high pressure fault in the compressor, switch LPS or switch HPS will open, the coil of switching device S will be de-energised and the power circuit broken.The same result will follow from a break in the control circuit caused by opening of the temperature sensor K, a control power failure or the failure of the control circuit fuse F.

Warning Circuit This circuit is arranged to generate a warning that the compressor has ceased to operate despite the fact that the switch IBS is closed. Except for that part of the warning circuit intended to warn of a failure of the power circuit, the warning circuit is supplied by an auxiliary warning power supply within the unit and by which a 24 volts direct current is applied to terminal 2 to ensure that warning will be given of a failure of the control circuit or its power supply. The warning circuit includes an audible alarm A and warning lamp L1 connected in parallel between line 11 and the common neutral line 5. A switch AS in the circuit of alarm A may be used to deactivate the alarm but lamp L1 will continue to indicate a fault condition.Current may be supplied to line 11 by any of three lines 6, 8 and 10, that is by line 6 in the even of a control power failure, by line 8 in the event of a fault sensor operation, and by line 10 in the event of a power circuit failure. The flow of current through lines 6 and 8 is controlled by a group of relays R4 to R7 which respond to the condition of the control circuit at various locations, current flowing through each of these relays to the neutral line. Thus, relay R4 is connected to the positive side of switch IBS, relay R5 to the neutral side of the switch IBS and relay R7 to the positive side the coil of the switching device S. Relay R6 is disposed in a line 7 between terminal 2 and neutral line 5, the line 7 also including contact R5a.

Contact R4a is held open while relay R4 is energised, so breaking the circuit through line 6 between terminal 2 and the line 11. Contact R5a is held open while relay R5 is energised to break the circuit through line 7 so de-energising relay R6. The line 8 between the terminal 2 and line 11 includes the contacts R6a and R7a, the former being closed and the latter open while the control circuit is operating normally. Finally, the line 10 includes the contact R3a (which is held open while the power circuit energises relay R3) and a diode D to prevent the flow of current from the terminal 2 into the control circuit.

Monitoring Circuits The monitoring circuits provide, on the one hand, an indication of the reason for an unintentional shut-down of the compressor in conjunction with the visual and audible warning described and, on the other hand, an indication of a failure of the auxiliary power-supply or potential pressure fault condition.The monitoring circuits include the neon lamps L2 to L8 which provide indications as follows: L2 low pressure fault L3 high pressure fault L4 control pressure failure L5 power circuit failure L6 potential low pressure fault L7 potential high pressure fault L8 auxiliary power failure Neon lamp L2 and L3 for indicating low and high pressure compressor faults are contained in respective monitoring circuits arranged to detect the opening of the associated switch and to cause the lamp to light provided current is present on the positive side of the switch. The monitoring circuit of switch LPS includes a relay R1 connected between the neutral side of the switch and the neutral line 5, and the monitoring circuit of switch HPS includes a relay R2 connected between the neutral side of that switch and the line 5. The contact of each relay is connected in series with the lamp, between the positive side of the switch to be monitored and neutral line 5. Both contacts R1 a and R2a remain open while current is flowing in the control circuit and the relays R1 and R2 are energised.

Openings of the switch LPS causes the relay R1 to become de-energised, closing of contact Tri a and lighting of lamp L2. Similarly, provided switch LPS is closed, opening of switch HPS results in the lighting of lamp L3 following de-energising of the relay R2 and closing of contact R2a.

Neon lamps L4 and L5 for indicating control circuit failure and power circuit failure respectively are included in respective monitoring circuits connecting line 5 to line 6 and line 5 to line 10 so as to light in response to de-energising of relays R4 and R3.

Neon lamps L6 and L7 for indicating low and high pressure potential faults are contained in respective monitoring circuits including switches LPS' and HPS' and connected between the neutral terminal of the associated fault switch and neutral line 5. Upon a potential fault condition arising, normally open switch LPS' or HPS' closes to light the associated lamp. Advantageously, a flasher unit is associated with the lamps L6, L7 to draw attention to the potential fault which, if not rectified, may lead to breaking of the control circuit with the consequences described above.

Neon lamp L8 is arranged in a line connected between the terminal 1 and neutral line 5 and normally broken by contact R8a of relay R8 connected between terminal 2 and the neutral line. Alternatively, this lamp may be included in a line connected between terminal 2 and line 5 in series with a push button switch for occasional manual checking of the warning circuit.

No monitoring circuit is provided in the unit depicted in Figure 2 to provide a specific indication of the opening of the switching device caused by a break in the control circuit following opening of the temperature sensor K, this being a relatively rare occurrence.

The operation of the complete control, monitoring and warning system will now be described in each of the various possible modes: Compressor Functioning Normally Figure 2 shows the various switches and contacts in the positions which they occupy when the compressor is functioning normally and the switch IBS is closed indicating a requirement for ice. Switches LPS, HPS are closed and switches LPS' and HPS' open. With current flowing through the control circuit from terminal 1 to the common neutral line, the coil of the switching device S is energised and relays R1 to R5 and R7 are energised and their respective contacts open.

Relay R6 remains de-energised and contacts R6a closed, because contact R5a is open and the circuit through line 7 between terminal 2 and the neutral line 5 is broken. The warning circuit and all monitoring circuits are therefore open.

When an ice bank of sufficient size has formed, switch IBS opens breaking the control circuit and opening the switching device S. Although relays R1 and R2 become de-energised, no current flows in the control circuit and lamps L2 and L3 cannot light. Relay R5 becomes de-energised contact R5a closes and the current flowing through line 7 energises relay R6 causing contact R6a to open.

Although contact R3a closes following loss of power in the power circuit, no current flows in line 10 because of the absence of current in the control circuit. Contact R4a remains opens and, in consequence, no current flows in lines 6, 8, 10 and ii of the warning circuit and the alarm A and lamp L1 remain unactivated.

Considering now the various faults which may occur: Control Circuit Power Failure A power failure may occur because of a fault in the control power supply or the failure of fuse F.

The absence of current in the control circuit results in the de-energising of relays R1, R2, R4, R5 and R7 and the opening their contacts. Switching device S also opens and the loss of power in the power circuit leads to the de-energising of relay R3 and the opening of its contact. The closing of contact R4a makes the warning circuit between terminal 2 and the neutral line 5 by way of line 6, line 11 and the alarm and warning lamp, and the monitoring circuit including lamp L4. Lamps L2 and L3 do not light, and therefore warning of power failure is given by the sounding of the alarm A and the lighting of lamps L4 and L1.

Low Pressure Situation As pressure falls, switch LPS' initially closes to light lamp L6. A subsequent fall in pressure opens switch LPS. Relays R1, R2, R7 thereupon deenergise, switching device S opens and the supply of power to the compressor is terminated. The closing of contacts Tri a completes the circuit from the positive side of the switch LPS through lamp L2 and back to neutral line 5. Lamp L6 is extinguished and L3 does not light because of the absence of current in the control circuit beyond switch LPS. Closing of contact R7a makes the warning circuit between terminal 2 and the neutral line by way of line 8, line ii and the alarm A and warning lamp Li. A low pressure situation is therefore indicated by the lighting of lamps L1 and L2.

High Pressure Situation As pressure rises, switch HPS' initially closes to light lamp L7. A subsequent rise in pressure leads to lamp L7 being extinguished and the warning circuit being made in the same way as described for a low pressure situation but in this case it is lamp L3 which light because of the closing of contact R2a.

Power Circuit Failure Loss of current in the power circuit causes the relay R3 to be de-energised and contact R3a to close. Control current is present at the positive side of the switching device and flows to the neutral line by way of line 10, line 1 1 and the alarm and lamp L1, and by way of the monitoring circuit including lamp L5.

Auxiliary Power Failure Relay R8 de-energises, contact R8a closes and lamp L8 lights. Modifications may be made to the circuit described above. Thus, for example, the circuit may be re-arranged to carry out the same functions in a different way or with different circuit elements. Thus, for example, the monitoring and warning circuits may be combined to form a single warning and indicating circuit. Alternatively the fault sensors may serve to energise relays, the contacts of which are included in the control circuit, wholly within the unit U. With such a control circuit arrangement, each such relay might have a further contact which closes to make a respective monitoring circuit when the control circuit opens, and possibly, a third contact which closes to make an alarm circuit.

Although an electro-mechanical unit is preferred, the same or similar functions may be carried out using in part solidstate or other electronic components.

Although it is preferred to have both high and low pressure sensors the compressor may be provided with a sensor or sensors responding only to one such abnormal condition. Likewise, although it is desirable for specific indications to be given of at least a low pressure situation and high pressure situation, the circuit may be simplified by omitting one, more, or all of the monitoring circuits. In particular, lamps L6, L7 may be omitted so that no warning of a potential fault is given. Or lamps L2, L3 may be omitted and switches LPS' HPS' connected to the neutral sides of switches LPS, HPS, so that one of the lamps L6, L7 lights when a potential fault occurs and remains alight following the fault materialising at which time alarm A sounds. Lamp L1 may be omitted, the visual indication being given solely by the appropriate monitoring lamp.

Although switches LP' and HP' have been shown as normally open, normally closed switches may be used in their place and energise relays holding open contacts in lines from the control or warning circuits in which lamps are included.

Although the unit described above has been designed exclusively for a bulk milk tank, it may be adapted to other refrigeration systems by, for example, using a thermostat in a cold store to open and close switch IB.

Claims (4)

1. In combination, a bulk milk tank associated with a container for a quantity of water, a refrigeration system for promoting the formation of an ice bank from the water, a control system for the compressor of the refrigeration system, the control system including means responding to the size of the ice bank to make and break the power circuit for the motor driving the compressor, and means responding to an abnormal pressure within the refrigeration system to terminate the supply of power to the motor, and a system for providing a warning of the interruption in the operation of the compressor.

2. In combination, a bulk milk tank associated with a container for a quantity of water, a refrigeration system for promoting the formation of an ice bank from the water, a control system for the compressor of the refrigeration system comprising means responding to the pressure within the refrigeration system falling below a predetermined minimum, means responding to the pressure within the refrigeration system exceeding a predetermined maximum, means for terminating the supply of power to the motor of the compressor of the refrigeration system upon operation of either of said means, means for providing a warning of an interruption in the power supply to the motor of the compressor caused by operation of either pressure responsive means, and means for indicating which pressure responsive means has operated.

3. A control, monitoring and alarm unit for the refrigeration system of a bulk milk tank, comprising terminals to which may be connected lines from the contacts of sensors responsive to the operation of the refrigeration system thereby to form a control circuit including a switching device for making and breaking a power circuit, a warning circuit including an alarm means, circuit elements for making the warning circuit in response to breaking of the control circuit by the opening of the contacts of selected sensors, and an auxiliary power supply for the warning circuit.

4. A refrigeration system including a compressor, first and second low pressure sensors associated with the refrigerant intake to the compressor, first and second high pressure sensors associated with the refrigerant discharge of the compressor, a control circuit including normally closed contacts, one of which opens in response to operation of the second low pressure sensor and the other of which opens in response to operation of the second high pressure sensor, a normally broken warning circuit including an audible alarm, means for completing the warning circuit in response to opening of either of said normally closed contacts, and potential fault indication means adapted to respond to operation of said first sensors, said sensors being so arranged that the first sensor of a pair operates before the second sensor during the development of an abnormal pressure condition.