Explanatory :

• A : Telescopic sight.
• B : Scale choice, 700 à 1500 °C or 1200 à 2000 °C.
• C : Cylinder receiving two batteries of 1.5 V.
• D : Trigger to switch on the pyrometer.
• E : Wheel of rheostat to control intensity of electric current in the filament.
• F : Eyepiece, telescopic sight .
• G : Dial.
• H : Zero setting button for galvanometer.
• I : Antiglare and anti-infrared filter.

The E rheostat allows to vary the intensity in the filament of the measure lamp. The measure is obtained at the disappearance of the filament whose hue is confused with that of the incandescent object, giving the impression of a clear cut filament.

The intensity in the filament is then the measure of temperature. This measure is obtained by direct reading on the galvanometer dial with two scales of measurement: 700 to 1500 °C and 1200 to 2000 °C. As with any measuring device, the best accuracy is obtained in the last third of the dial: select the measurement scale accordingly.

Measurement procedure :

• Check the zero of galvanometer. If necessary, adjust using the H button.
• Deploy the telescopic sight A and the eyepiece F.
• Choose a scale with the help of B.
• Aim the target and press the D trigger.
• Eventually, adjust sharpness by playing on the position of the E eyepiece and the A telescopic sights.
• Use the I red filter if the target is too bright for your eyesight.
• Gradually increase the intensity of electric current in the filament using the E rheostat.
• When the filament seems to blend into the target, one said it had disappeared. Then read the temperature of the target on the G dial.
• Mission accomplished, you can release the trigger.

Interesting Link :

• Institut für Energieforschung und Physikalische Technologien : Very nice photographs of a H&B pyrometer in good shape.