Instrumentation for the automatic control of pH in the laboratory applications
This apparatus forms a complete integrated system for the automatic control of pH in laboratory scale chemical reactions.
Addition of acid or alkali to the reaction vessel is controlled via miniature stepper motor driven peristaltic pumps. The instrument provides digital indication of pH with a resolution of 0.01 pH, adjustable 3 term control of the pump rate, with appropriate drive electronics for two pumps. Facilities for manual control of each pump i.e. start/stop, speed and forward/reverse are provided and may be used to prime the system before use. The pumps used are the standard Measurement & Control peristaltic pump heads with integral stepper motor.
The system apparatus can be configured to accommodate a variety of conditions e.g. either pump can be arranged to pump acid or base as required into the reaction vessel, pump No.1 will be automatically controlled and pump No.2 will feed at a manually set rate. The flow rate of the controlled pump being a function of the instrument set point pH value and the measured pH value obtained from the pH probe.
Where a system is generating either acid or base, then it is possible to dispense with the fixed addition of acid or base via pump No.2 (constant flow rate pump) and only use one pump with the instrument (i.e. controlled flow rate pump) to achieve satisfactory control. A typical application may be to hold a reaction at pH 7.
The pH instrument employs advanced microprocessor technology to provide the following features:
The instrument is calibrated using standard 4, 7 and 10 pH buffer solutions. Normally a combination pH probe is supplied with a co-ax connector. An additional temperature sensing element is required if Automatic Temperature compensation is used. (ATC compensation range -150C to 1200C).
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