GB2051370A - Hot water tank temperature sensing system - Google Patents

Abstract

A hot water tank temperature sensing system having a plurality of sensors 10 for mounting at different vertical locations on a hot water tank 11. Each sensor is coupled to a comparator 13 and all the comparators are supplied with a common signal from a control 15 representing a predetermined temperature. Indicators such as light emitting diodes 16 are connected to the outputs of comparators 13 to indicate when the water at the levels at which the sensors are located have reached or exceeded the predetermined temperature. <IMAGE>

Description

SPECIFICATION Hot water tank temperature sensing system This invention relates to a hot water tank temperature sensing system.

With industrial and domestic hot water tanks it is often difficult to assess the amount of water in the tank that is at or above a desired temperature, particularly if the tank is lagged.

In consequence it is an object of this invention to provide a system which will provide indications of the temperature of the water at different levels in the tank.

In accordance with this invention therefore we provide a sensing system comprising a plurality of temperature sensors for mounting at different levels on a hot water tank, each sensor providing an electrical potential representing the temperature of the tank at the location of the sensor, and comparison means fed with a signal representing a predetermined temperature and the potentials for the sensors to provide for each level at which a sensor is located, a signal indicating that that level is at a temperature at or above said predetermined temperature.

In order that the invention may be fully understood, a preferred embodiment thereof will now be described with reference to the accompanying drawings in which: FIGURE 1 is a block schematic diagram of a hot water tank temperature sensing system in accordance with this invention; FIGURE 2 is a circuit diagram of a sensor voltage amplifier used in the system of Figure 1; FIGURE 3 is a circuit diagram of the temperature and select buffer amplifier of the system of Figure 1; Figure 4 is a circuit diagram of a comparator used in the system of Figure 1; and Figure 5 is a circuit diagram of the relay driver used in the system of Figure 1.

Referring now to Figure 1, the system comprises three temperature sensing junction diodes 10, each located on a hot water tank 11 at different levels, the diodes feeding potentials representing the temperatures at the different levels to three sensor voltage amplifiers 1 2 whose outputs are fed to three comparators 13 each of which also receive a signal from a temperature select buffer 14, the signal representing a predetermined temperature as set by a select control potentiometer 1 5.

Each comparator compares the potential from the associated sensor voltage control amplifier and produces an output signal if that potential represents a temperature at or above the temperature represented by the signal from the buffer 14. The output signal from each comparator is fed to an L.E.D. 1 6 so that a visual indication showing whether at each level of the tank at which a sensor is located, the predetermined temperature has been reached.

Figure 2 shows a circuit for the sensor voltage amplifiers each comprising a differencing amplifier 20 having an input 21 coupled via a resistor R6 to the output of a sensing junction diode 10 and via a resistor R5 to the output 22 of the differencing amplifier, a variable resistance PR1 coupling the second input 23 via a fixed resistor R4 to a voltage source V2. An increase in temperature at the diode 10 causes the current through R6 to fall resulting in an imbalance between the currents through R6 and PR1 thereby increasing the output voltage V3 of the differencing amplifier 20. Thus more current flows through R5 and the diode 10 increasing the potential applied to the input 20 until the currents through R6 and PR1 are approximately equal.

The gain of the circuit is selected so that a 400C change in the predetermined temperature results in a change from +2 volts to +8 volts in the output voltage of the differencing amplifier 20 which is fed to an input 41 via a resistor R8 of a comparator 1 3 as shown in Figure 4 together with a signal from the buffer 14, shown in Figure 3 which is applied to an input 42 via a resistor R7.

The comparator 1 3 operates on the current differences between the two inputs, a resistor R9 being coupled between the input 41 and an output 43 via a resistor R10 to provide a small degree of hysteresis to ensure predictable operation.

An L.E.D. 1 6 is connected between the junction of R9 and R10 and ground so that when a voltage at the output 43 reaches or exceeds a value representing the predetermined temperature set by the potentiometer 15, the L.E.D. emits light, A circuit for the temperature select buffer 14 is shown in Figure 3. The purpose of the amplifier is to buffer the potentiometer 1 5 chain comprising resistors R1, VR1 and R2 from the effects of varying loads imposed by the three comparator circuits 1 3 and enables the potentiometer current to be kept low.

An output from each comparator is fed to a relay driver 50 shown in Figure 5, the output 51 of the relay driver being applied to a relay coil 52 for operating two sets of contacts 53 and 54 (see also Figure 1). The relay driver is used to provide sufficient current for the relay which is not readily available at the output of each comparator. The relay driver can be set to operate the relay when only the lowermost (in Figure 1 ) comparator produces an output, i.e. when only the lowermost L.E.D. is lit, or when the uppermost comparator produces an output lighting the uppermost L.E.D.

If set to operate only when the lowermost L.E.D. is lit, the contacts 53, 54 can be used to switch on an immersion heater to further heat the water in the tank. Alternatively the contacts (or additional contacts) may be used to switch on a water circulation pump coupled to the tank when one or more of the comparators produces an output.

Although only three sensors are illustrated in Figure 1 many more could be used if it was required to check the water temperature at more than three levels. Also a multiple threshold circuit may be used instead of the three separate comparators described and illustrated in the drawings. Furthermore forms of indication other than L.E.D.'s may be used such as relays energising lamps, or a meter may be used calibrated in CC.

Claims (6)

1. A sensing system comprising a plurality of temperature sensors for mounting at different levesl on a hot water tank, each sensor providing an electrical potential representing the temperature of the tank at the location of the sensor, and comparison means fed with a signal representing a predetermined temperature and the potentials for the sensors to provide for each level at which a sensor is located, a signal indicating that that level is at a temperature at or above said predetermined temperature.

2. A system as claimed in Claim 1 including, for each sensor a comparator; the comparators being fed with a common signal representing said predetermined temperature, and each comparator being fed with a signal from the associated sensor representing the temperature of that sensor.

3. A system as claimed in Claim 2 including a plurality of light emitting diodes, each associated with a different comparator and energisable by the indicating signal produced by that comparator.

4. A system as claimed in Claim 2 or Claim 3 including a driver unit coupled to said comparators to provide an actuating signal upon receipt of an indicating signal from a predetermined one of said comparators.

5. A system as claimed in any one of Claims 1 to 4 including for each sensor, a sensor voltage amplifier.

6. A hot water tank temperature sensing system substantially as described herein with reference to the accompanying drawings.