GB904490A - Improvements in titration apparatus - Google Patents

Abstract

Automatic titration apparatus, particularly for measuring the hardness of water, comprises a measuring chamber 6 in which a sample of water to be tested is taken from a supply pipe 14 and a measuring chamber 4 which draws precise amounts of test solution from a reservoir 1 and adds it to the sample. As described, the hardness of the water is measured by a photo-cell arrange <PICT:0904490/III/1> ment or by a soap solution test but the apparatus may be used for titrations by colorimeter or pH meter or analysis by absorptiometer or conductivity methods. A sequence controller 20 having a number of thermionic-valve-controlled relays controls the automatic operation of the apparatus; the circuit and setting-up procedure for the controller are described. On receipt of an initiating impulse from the controller 20, a valve 18 closes to shut off a pipe leading the water to waste and the valve 16 opens to allow the water to rise to the level of the electrode 12 in the chamber 8, when the valves 16 closes and the valve 18 is opened again. At the same time as the valve 16 opens, the valve 3 opens and a test solution, comprising disodium ethylene-diamine-tetra-acetic acid, a buffer and an indicator and contained in a reservoir 1, flows into the chamber 4. When the test solution reaches the electrode 6, valve 3 closes and a series interlock circuit dependent on valves 3, 16 and 18 is closed and opens valve 7 until the solution just clears electrode 5. At the same time as valve 7 opens, a stirrer 21 mixes the solution and water together and then stops. After a period in which the mixture is allowed to settle, a lamp 9 and photo-electric cell 10 detect the blue or red colour of the solution and operate indicators and, if required, alarms in the controller. Following the test, valve 17 opens to discharge the mixture to waste until, when it clears electrode 11, the valve 17 is closed, valve 18 is closed and valve 16 is opened to allow rinsing water to flow into the chamber until it reaches electrode 13. Valves 18 and 16 are then opened and closed respectively and valve 17 opened to allow the rinsing water to run to waste until it clears electrode 11. To assist in rinsing, the electrode 12 starts the stirrer when the water reaches the electrode and stops the stirrer when the water clears it. When the rinsing water clears the electrode 11, an adjustable timing circuit is switched on in the controller and after a predetermined time another initiating impulse is given to the apparatus. When the soap solution test is used, a fourth electrode is provided above the electrode 12 and, when the solution and water are stirred, the lather bridges the fourth electrode and the water so that a bias voltage is applied to a thermionicvalve-controlled relay. If the water is soft, the lather persists during a period set by the controller but if hard the lather quickly collapses and these two conditions are indicated in the controller. Indicator lamps indicate the stages reached in the test and inter-locking circuits make each stage dependent on completion of the preceding one. The lamp and photo-electric cell circuit are automatically checked prior to each test. If the test sequence is stopped at any point, a monitor alarm 23 is operated and this alarm can be used to switch over to a standby apparatus.