DE1516074B2 - PHOTOELECTRIC EXPOSURE METER WITH BRIDGE CIRCUIT - Google Patents

Description

in the middle measuring range. The supply voltage is controlled in such a way that with each illuminance acting on the photoresistor R _ph , ie with each bridge ratio

the same bridge sensitivity results.

In another embodiment (see FIG. 2), the wiper 11 of the potentiometer 10 is coupled to the adjusting axis 7. The two ends of the potentiometer 10 are jointly connected to one pole of the power source 1, while the center tap of the potentiometer 10 is connected to the other pole of the power source 1 via a resistor 12.

The mode of operation is essentially the same as in the embodiment according to FIG. 1. When turning of the adjuster 8 for the purpose of bridge adjustment, the wiper 11 moves from one end of the potentiometer 10 to the other end, with the full voltage of the power source at both ends, but at the center tap a voltage reduced by the voltage drop across the resistor 12 is removed.

1 sheet of drawings

Claims (4)

1 2 value of the measuring range prevailing minimum sensitivity. The object of the invention is to change the 1. Photoelectric exposure meter with feed voltage for a measuring bridge, the middle bridge circuit of which, the feed voltage of which corresponds to the maximum sensitivity in terms of measurement value; the dependency on the setting of the tuning counter-invention aims to increase the consistently level can be changed by a potentiometer, constant bridge sensitivity at measuring, characterized in that with the bridge with a single large measuring range.
Sliding contact (9) of the tuning resistor (13) According to the invention, this is achieved in that an adjusting device (7) for the potentiometer (3; io with the sliding contact of the tuning resistor 10) is coupled, with its adjusting movement from the initial position via a middle position into which is, with the adjusting movement from the starting position end position the supply voltage from an upper over a middle position to the end position the extreme value over a lower extreme value like supply voltage from an upper extreme value over the to the upper extreme value continuously 15 a lower extreme value again is changeable on the upper one. Extreme value is continuously changeable. 2. Photoelectric light meter according to Preferably the potentiometer slider is over Claim 1, characterized in that the Po- is coupled to the sliding contact and as a cardiac tentiometer grinder (4) adjustable via a control cam formed with the sliding cam. One Kontakt (9) coupled and as a heart curve, according to another embodiment of the invention, this is the case formed control cam (5) is adjustable. Potentiometer with both ends on one pole 3. Photoelectric light meter after the power source and with its center tap over Claim 1, characterized in that the Po- has a resistor at the other pole of the current tentiometer (10) with both ends on the source. It is useful for brightness measurements one pole of the battery (1) and with its Mit- 25 a branch of the bridge circuit a photoelectric "ten tap - via a resistor (12) on the resistor, the supply voltage of the the other pole of the battery (1). ^ Bridge depending on the 4. Photoelectric exposure meter according to setting influencing settings for aperture, Beden claims 1 to 3, characterized in that the exposure time, film sensitivity, etc. can be changed in that a branch of the bridge circuit is a photo-30. The details of the invention are based on electrical resistance (R _ph ) and are illustrated by exemplary embodiments. It shows
Supply voltage of the bridge circuit as a function of F i g. 1 the voltage divider and can be influenced by the tuning resistor (i? ₃ ; .R _{4) via a symmetrical control curve}
influencing adjusters (8) for aperture, Beiich- F i g. 2 a voltage divider with center tap,
processing time, film speed, etc. can be changed 35 The measuring bridge is made up of the photoresistor. R _p! " The fixed resistor R ₂ and the adjustable resistors R ₃ and i on the tuning resistor 13?" ₄ formed. The fixed resistance R ₃ corresponds to known way to the geometric mean of the resistance 40 values of the photoresistor R _ph , so that this determines the maximum sensitivity of the measuring bridge. The invention relates to a photoelectric existing resistance ratio of R ₃ : i? ₄ = 1 light meter with bridge circuit, whose feed prevails, since the sliding contact 9 in the electrical voltage depends on the setting of the center of the tuning resistor 13. In the diago- The tuning resistor, which is designed as a zero instrument, is connected through a potentiometer is changeable. Measuring mechanism 14. Above the switch 2 activated To compensate for the sensitivity curve in the switchable current source 1 there is a potentiometer 3 measuring bridges, arrangements are known in which (see The cam 5 sits with a tuning curve 6 to the sliding contact of the tuning resistor to control the sliding contact 9 for the AbPotentiometer or a switching contact to the switching resistor 13 on an adjusting axis 7 is coupled to an adjuster 8, which is the. In these arrangements, a sum gear to enter the Berung with the amendments is driven by the Abstimmwiderstandes from one extreme 55 glade factors aperture K, exposure time t and value to another one in the same direction progressive other factors χ such as film sensitivity and change of the supply voltage, so that the course filter factor represents. ■ the bridge sensitivity one of the change in the resistors R ₃ and R _{4 of} the tuning resistor in each case rectified Ten-Stand 13 allow, the bridge has at difference. With this measure, the supply 60 borrowed illuminance and the voltage dependent thereon with regard to the equalization of the different values of the photoelectric bridge sensitivity can only be changed for those measuring resistance R _pU by turning the adjusting axis 7 whose first limit value is the same. The measuring bridge corresponds to the common maximum sensitivity. Axis 7 the cam 5 for the grinder 4 of the one to be achieved consistently constant bridge 65 potentiometer 3 and the tuning curve 6 for the kenensensitivity is based on the sliding contact 9 of the tuning resistor 13 possible exclusively falling tendency of the rotates, so that with changing the Tuning bridge sensitivity after the one at the other limit resistance, a reduction in the supply voltage