The invention relates to a heat transfer meter of the kind defined in the preamble of the attached main claim.

In recent years it has been more and more important to dimension the insulation of buildings in an economical manner. V/ith increasing costs of heating it has been neces¬ sary to check and to improve such an insulation. For this purpose different methods of measuring the heat transfer in walls have come into use. One has, then, tried to survey the heat transfer at differnt places of a wall, and heat cameras have for instance then been used. This has proved that there will ofren be heat leakages in the walls, which leakages one has not been able to prove earlier in a suffi¬ ciently evident manner. Said method has, however, the dis¬ advantage that it requires a circumstantial equipment and is relatively expensive,,

It is therefore desirable to be able to measure heat transfer in a simple manner and to be able to survey the heat transfer in whole wall areas, windows or doors. For that purpose the meter should be simple to bring along, simple to operate and it should rapidly give measuring results. The invention relates to a device for making this possible.

The solution which is suggested according to the in¬ vention is apparent from the characterizing portion of the attached main claim.

According to the invention an electronic amplifier is used which forms the quotient between the inner temperature minus the inner wall temperature on one hand and the inner temperature minus the outer temperature on the other hand, the temperature values of the first subtraction being ob¬ tained by means of thermal elements , which are connected to the device, and the difference according to the second sub¬ traction being adjustable in a feed-back circuit of the amplifier, the output quantity of which is supplied "bo an instrument graduated in heat transfer coefficient k.

The invention thereby starts from the following re¬ lation between the heat transfer coefficient k and the tem¬ perature which incluences the measuring: k = A (t.-t ) / (t.-t ) /m ² °C where A is a quantity which is the sum of the heat transfer coefficients for radiatiion and for convection and where t. is the inner temperature in a room where the measuring is pe formed,t is the inner wall iremperature in said room and t is the outer temperature outside the wall inside which the measuring ^σ is made. The difference t.-t,u, is measured with co mon thermometers and the corresponding number of degrees can for instance be adjusted with a graduated knob as a feed bac value of the amplifier. The difference t I.-t is obtained by ^J means of thermal elements, which are connected to the devic according to the invention.

The invention will be described more in detail in con¬ nection with the enclosed drawing, which shows an amplified 1 , for instance an operational amplifier, which is fed from a current source 2 and the output of which is connected to an instrument. The amplifier has a feed-back circuit, here shown as a voltage divider with the -res ^* is1:ors 4 , 5 and 6 , of which the resistor 5 is a potentiometer, from the tap of which the feed back quantity is derived. The difference between the voltages from two thermal elements 7 and 8 is supplied to an input on the amplifier. One thermal element, 7, is mounted in the housing of the device shilst the other thermal element, 8, is mounted in a probe tip, 8, which is connected by a conductor to the input circuit of the ampli¬ fier. Through a suitable choice of the shown and implicit circuit elements of the devide, which latter need not be described in detail for the understanding of the mode of operation of the invention, the relation according to the said equation- can be realized with the required accuracy and the heat transfer coefficients k can be read directly on the instrument 3.

With the device one can measure the heat transfer coefficients k by aid of the probe and can survey the heat transfer in a wall, a door or a window.

OMPI