Circuit arrangement to ascertain and indicate that a luminous density limit condition is exceeded

Claim 1

A circuit for determining and indicating that a luminous density limit is exceeded, comprising: photoelectric diode means for producing a diode signal indicative of an incident luminous density; means, arranged to receive said diode signal, for producing a logarithmic signal having an amplitude corresponding to the logarithm of the amplitude of said diode signal; circuit means for generating a determinable limit value signal, said circuit means having an adjustable temperature dependent circuit comprising a potentiometer having a tap and also comprising a temperature-dependent dividing circuit connected to said potentiometer; and comparator means having a first input and a second input, said first input being connected to receive said logarithm signal and said second input being adapted to receive said limit value signal for comparing said limit value signal and said logarithm signal and for producing a control output signal when said logarithm signal and said limit value signal fail to satisfy a predetermined relationship, said control output signal being applied to an indicator circuit and a processing stage.