DE465638C - Method for temperature control of electrical heating devices - Google Patents

Description

It is known to regulate the temperature in heating devices in that their Heating resistors are connected in series with a separately heated heat switch, and that the heating of this Thermostat is regulated:

The heat conditions in such a temperature control result from the following consideration: In Fig. Ι let ι a heat switch provided with a heating coil, which has the property, at a constant temperature t. ₂ switch off. Furthermore, let 2 be the heater; the heating coil of the heater 2 and that of the heat switch are switched off together by the heat switch. The thermal energy given off by the thermal switch 1 to the heater is:

the one given off by the heater to the surrounding space: A = K (ί ± - ^ o)> where a, A represent amounts of heat energy. ^ ₁ is · the temperature of the heater and t ₀ that of the surrounding room. K, k are constants which depend on the heat transfer coefficients and the surfaces of ι and 2. The quantities a, A simultaneously represent the amounts of electrical energy developed in the heat switch 1 or in the heater 2 during continuous operation.

The ratio of heater power

AK t _x - 1 ₀ For a medium temperature

(I)

will

! and if a _{m represents} the value of α belonging to t _m ,

If the heat switch is set to a switch-off _{temperature of ί 2} = 8ο ° and the room temperature is ^ ₀ = SO ⁰ , then

= 50 ⁰ .

the mean temperature t _m =

K and k are constants, nothing is changed in A either. The temperature of the heater should be regulated by changing α.
It will:

b t f

/ ν μ In tit

or with

^{k K}

From this it follows
for S ₁ = 75 «75 ⁼⁼ *» «“. "^ ~ 0.91 · Αϊ,»

, ... ο 8 ° - 25

1 ^{J 2S m} 25 - 20 that is, the supply to the heat switch

Energy must be in the ratio of

0.091

= 121,

that is, by 121 times, in order to achieve a temperature control from 75 ° to 25 °. Nothing stands in the way of supplying less energy to the heat switch. In order to reach the temperature t _x = t ₂ , a = zero must be made. The conditions are less favorable if the amounts of energy supplied to the heat switch have to be selected to be very large in order to achieve lower temperatures. The heat switch switches off after the actual switching elements have reached the setting temperature. It is now not feasible to apply the heating winding directly to this, since the switching then takes place too quickly; therefore, there is a risk that the heating coil of the thermal switch assumes an unacceptably high temperature at high energy supply, which the winding cannot withstand and which is also used for certain heating devices, eg. B. electric heating pads, becomes dangerous. These conditions are particularly unfavorable when the heaters are used within larger voltage ranges, e.g. B. between 110 and 150 or even between 110 and 220 volts should work.

It can then easily happen that the heating coil of the thermal switch is inadmissible heated up or even burned before the double metal strip could switch off. on the other hand it is naturally of great technical advantage within larger voltage ranges to be able to use the same devices.

The invention aims to eliminate this difficulty so effectively that the Temperature regulation on the one hand with large temperature ranges and on the other hand too can be used for large voltage ranges.

From the formula τ given above, t _i results in:

It follows that it can be depressed t ₁ both by magnification of α as well as by reduction of A, or that the energy of heat switch may be a smaller dimensioned in reduction of the energy of the heater A, in order to achieve the same.

The invention consists in applying this knowledge; H. the temperature of a The heater with a separately heated heat switch is regulated downwards as a result, -65 that with constant or increased heating energy of the heat switch the one of the heater is reduced.

In the case of electric heating pads that are equipped with heat switches, it is known to change the heating energy by switching the resistors. However, this can do not lead to a temperature regulation in the actual sense; because such Heating pads still reach the maximum permissible even at a greatly reduced maximum temperature Switch-off temperature of the heat switches, if they are covered so well that the heat dissipation is low.

This is especially true when heating pads are made for a wide voltage range should, i.e. when heating pads, which are built for 110 volts, also work on 220 volts should. Such a heating pad would, for example, be 60 watts when connected to 110 volts on position III, 30 watts on position II and 15 watts on position I. In connection at 220 volts it would then have 240 watts in position III, 120 watts in position II and 60 watts to position I. A change in the switch positions would not be able to bring about a change in temperature at all, since this heating pad when connected to 220 volts in position I, the power that the 1 io volt heating pad on the Position III takes up, since 60 watts will almost always be enough to put the heating pad on the Bring maximum temperature. In this case, temperature control is only special heated thermal switch is possible at all. The control of the heating energy has so in heating devices with heated heat switches a completely different effect than with simple unheated heat switches.

Fig. 2 shows an embodiment of the invention. Let W ₁ and W ₂ be the heating resistors of the heater, 5 and 6 the heated heat switches. The heat switch 6 carries the heating winding W ₁ , the heat switch 5 the two heating windings W ₂ and w. _& . The resistance W ₁ can be equal to the resistance w _s . Both heat switches can be set to the same switch-off temperature. The circuit can be changed using switch 7. The parts 8 are rotatable relative to the rest of the switch and connect the contacts 9 in various ways. In the table Fig. 3, the connections made in the various positions o, I, II and III of the switch of the plus and minus ^ -Poles with the four lines A ₃ B ₃ C and D are given. In place

465688

treatment III, the resistors W ₁ and W _{2 are} connected in parallel. A thermal switch resistor W ₁ or w _{s is} in series with each of the resistors. The heating energy of a heat switch at the HT position. and those of the total main heating energy A _1n are:

and

Here i is the root mean square value of the heating current, which results from the connection value of the current calculated from voltage and resistance, multiplied by the time during which it is switched on by the heat switch in a certain observation time, divided by the observation time.
It will also

on W ₃

On the 2 w ₁

assuming that W ₁ = w ₃ and W ₁ - W ₂ . In position II only the main heating resistor W _{1 is} switched on. It will then

au = in ² w ₃ , An = i _n ^{2 ψ} ι ψ ~ = ψ '

that is, twice the ratio - ^ -. In

Position I, W _{1 is} connected in series with W ₂ , and it results

(ti = - ii ² (w _z + W ₃ ), Ai =. ii ² -2-W ₁

so

ai __ W ₂ -f w ₃ A ₁ ~ 2W ₁ '

If W ₂ = S W _{3 is} assumed, then
ai 3w _s

so

aj

3JW _ 6 am Au

At the '

To determine how the energy values behave, which on the one hand in the heating winding of the heat switch when starting a

5Q heating pad, which is only regulated by increasing the heating resistance of the heat switch, compared to a heating pad according to the present invention, the connection energy values of these two circuits are to be compared here. In this case, it is not the time average values given above, but the full connection values, since the controllers are fully switched on for a certain time when the cushion starts up. The currents then flowing are denoted by 7. If the main heating resistance were not to be changed in order to achieve the same differences, the connection values, which are designated E ₁ , E ", JS ₃ , would be proportional to the values calculated above (Z ₁ , Ut ₂ , a _s , so that the following relationship results:

Ei : En: Em = «/:« //: «/// = 1: 3: 6

Em would have become = 6 egg . While the new circuit results in:

■ ^E i _ 4 "_ 3

So ZT _{1 would} only be 50 ⁰ O larger than Ε _Λ . This makes it possible to overload the heater very considerably with higher voltage, since the heat switch heating can be kept relatively low under all conditions.

When changing from position III to II, only the energy A of the heater was changed, while when moving from position II to I, both A and α were changed. In both cases, a substantial reduction in thermal switch heating energy was achieved.

The specified circuit and the size ratios of the resistors are only given as examples. The resistors W ₁ and W ₂ , as well as the resistors W ₁ and w _s, can be different from one another. The switch-off temperatures of the heat switches 5 and 6 can also be different from one another. Instead of the resistor W ₂ , a third thermal switch 10 with a high resistance W _{2 can also be switched} into the supply line B , as shown in FIG. The heat switch 10 could be set for other switch-off temperatures than 5 and 6. The same purpose can also be achieved with completely different circuits if the energy of the heater is changed only when using heated heat switches, for the purpose of reducing the heat switch heating energy.

The resistance W ₂ must, in the circuits according to Fig. 2 and Fig. 4, be considerably greater than the resistance w _s . For example, if the heating pad according to Fig. 4 were to be connected between A and D , the temperature would not go down, especially when connected to 220 volts, although the connected load would be reduced by half. Rather, a decrease in the connection value would lead to an increase in temperature, because by increasing the resistance (from

W ₁ to [W ₁ + W ₂ ]) the ratio of the thermal switch heating to the cushion heating is influenced in such a way that, according to the above, the temperature must go up. Therefore, in order to achieve a decrease in the temperature rather than an increase in temperature at the lowest temperature level, the resistance value must be increased from W ₃ to (w ₂ - \ - W ₃ ) and thus significantly

ίο be set higher than W ₃ . The fact that a reduction in the connection value does not correspond to a temperature decrease in the new circuit under all conditions shows at the same time that the measure which, in a certain limited manner, leads to the goal in the known heating pad circuits does not necessarily apply to a heating pad circuit with heated ones Controllers may be transferred, but that this is only possible under the conditions on which the present invention is based.

Claims (3)

Patent claims: i. Method for temperature control of electrical heating devices · by means of separate heated thermal switch, characterized in that the transition from the higher to the lower temperature the ratio of the heating energy of the heat switch to that of the heater is increased in that the Device heating energy either on its own or with simultaneous enlargement the heating energy of the thermal switch is reduced. 2. The method according to claim 1, characterized in that for the lower temperature levels in the heater, a heat switch (10, Fig. 4) with heating resistors so high ohms (w ₂ ) is switched on that the heating energy of the heat switch is higher when the device heating current is reduced. 3. The method according to claim 1, characterized in that for the lower temperature levels in the heater heating resistors with such high ohmic numbers (Ot ₂ + W ₃ , Fig. 2) are switched on to the heat switch resistors that the heating energy of the heat switch is higher when the device heating current is reduced. 1 sheet of drawings