GB1288464A - - Google Patents

Abstract

1288464 Replenishing developer baths; automatic concentration control C S OST 4 Aug 1970 [11 Aug 1969] 37616/70 Headings G2A and G3R A test strip of film is exposed, and successive samples of developer from a developing bath are applied to successive portions of the film, which are then developed; the optical density of these developed portions is sensed, and further developer liquid from a replenisher supply is added to the bath in accordance with the sensed density. The test strip 10 is wound across from a supply reel (11), Fig. 1 (not shown) to a take-up reel (31), passing through an exposure station 13 and a development and monitoring block 23. The exposure station is shown in more detail in Fig.3, the film 10 being held by a pressure pad 14 against the upper end of a block having a cylindrical bore in which is disposed a lamp 16 and masking slits 17, 18. The block 23 has two cylindrical bores 71, 81, and the film 10 passes across the open upper ends of these bores, being held against them by a pressure pad 24. Bore 71 is divided by a spacer 70 into an upper compartment 74 and a lower compartment. A sample of developer from the main bath 92 is pumped into bore 71 via an inlet tube 33, where it passes upwards through gaps 72 in spacer 70 and so floods on to the film 10, leaving the bore again through an outlet tube 34. The monitoring bore 81 has a lamp 83, light from which passes through a filter 85, to render it non- actinic, and the film 10, to a densitometer head 84. The resistance of head 84 varies according to the intensity of light incident upon it, and this resistance forms one arm of a bridge circuit Fig. 9 (not shown). Fig. 8 shows the main developing bath 92, in which photographic film 90 is being processed. Liquid is pumped through a pipe 94 leading from the bottom of the tank past junctions with tubes 33, 34, through which the samples are taken to and returned from bore 71, and back to the bath. Before discharging into the bath, the pipe 94 is constricted into a Venturi 95, to which is connected a tube 96 leading to a replenisher supply 97. Between its ends tube 96 is enlarged into a flow chamber 99 in which are located a manually operated control valve 101 and a valve 103 controlled by a solenoid 104. If the test strip is insufficiently dense, the additional light transmitted reduces the photo-resistance of the head 84, which unbalances the bridge circuit. This causes the solenoid 104 to become energized, so opening the valve 103 and allowing replenishing liquid to be added to the bath 92. The circuit arrangement Fig. 9 (not shown) is such that the amount of added replenisher is proportional to the rate of decrease in the sensed optical density.