Time-operated devices for reflux control

These requirements are fulfilled by the author s mechanical timing device [11]. It has a contact disc driven by a synchronous motor the adjustment of the desired 

If the electronic relay is equipped with a switch to convert it from normally closed to normally open , the reciprocal reflux ratios (e.g. 1 2, 1 5 etc.) can also be obtained for coarse separations. 

The contact disc can be replaced by others yielding different periods. A more accurate control may, for instance, be provided in the range from 20 1 to 100 1 on the other hand the apparatus may be adapted for take-off times up to 30 secs, so that it can be used in pilot-plant and technical distillations. 

The timers functioning entirely on electronic principles allow take-off and reflux periods of 0.1 sec to 20 min. to be adjusted with an accuracy of 1% [56]. For an alteration of the reflux ratio they require a change to be made in both the take-off and reflux times. A number of electronic devices are commercially available most of which are provided with bubble-point control. The column head is set at infinite reflux ratio as soon as the pre-set temperature of the contact thermometer placed in the column head is reached. When the temperature falls below this threshold the preselected reflux ratio is automatically switched on again. As an example. Fig. 386 

The accuracy of reflux control by means of electronic timers has been thoroughly studied by Rock et al. [13]. Geinmecker and Stage [67] have found that constant, reproducible and load-independent values for reflux can be obtained only with elec-tromagneticaUy controlled components. Deviations may be due to the following effects. 

---