Photometer circuitry for the digital indication of the light absorption of a test sample

Claim 1

A photometer for providing an indication of the light absorption properties of a test sample comprising: test signal means (4, 5) for providing a first voltage proportional to the intensity of a light beam emerging from the test sample (3); comparison signal means (9, 10) for providing a second voltage proportional to the intensity of a light beam applied to the test sample; capacitor means including a capacitor (13), amplification means (10a) coupled to said comparison signal means (9, 10) and to said capacitor (13) for amplifying said second voltage by a predetermined amount and for applying same to said capacitor to charge said capacitor to a voltage in excess of said second voltage, said capacitor means including first sensing means (17) coupled to said capacitor (3) and said comparison signal means (9, 10) for initiating a discharge time period when said capacitor discharges to said second voltage, said capacitor means further including second sensing means (21) coupled to said capacitor (13) and said test signal means (4, 5) for sensing when said capacitor has further discharged to said first voltage for terminating said time period; and means (26) coupled to said capacitor means (13) for providing the discharge time period of the capacitor as an indication of the light absorbing properties of the test sample.