6.4 Softstart

Heating elements that have been standing for a longer time draw moisture. If they are heated up at full power, the stored water evaporates abruptly; the steam pressure bursts the insulation open from the inside. The heater then does not fail immediately but weeks later, with an insulation or current fault.

The softstart prevents this by first holding the channel at 100 °C. Water boils at this temperature and therefore leaves the heater as steam without a dangerous overpressure building up. Only after that does the channel continue heating to its set temperature. The temperature is therefore fixed and cannot be set – what can be set is the holding time, five minutes ex works.

Figure 19: The softstart holds the channel at 100 °C until the holding time has elapsed. The heat-up time is extended by this period.

The softstart only runs if it is activated for the channel and the set temperature is above the softstart temperature. A channel controlled to 80 °C has no softstart – it never gets beyond the critical limit.

When the softstart counts as done

The setting “Softstart (finished)” is not a specification but a display: it says whether the channel has already accumulated its holding time. The Thermonom counts this time whenever the measured temperature is above the softstart temperature – even if the channel is not in the softstart at all but has long been working at operating temperature or is merely cooling down slowly.

If, on the other hand, the temperature of the channel drops well below 100 °C again, the accumulated time lapses completely. This results in the behaviour that is noticeable in operation:

A tool that has stayed warm over the break heats straight through without a softstart. Moisture cannot have accumulated as long as the heater was hot.
A tool that has cooled down overnight goes through the softstart again, even though it already ran once yesterday.
After a mains failure the device checks the temperature: if the channel is still hot, it resumes operation without a softstart.

NOTE

During the softstart the channel does not report “operational”. An output that switches the injection enable therefore remains inactive until the softstart has ended – see Section 9.2.8, “Inputs and outputs”. The remaining time is shown by the channel detail view.

NOTICE

Do not switch the softstart off to save heat-up time. The minutes saved cost heating elements – and the failure does not occur while saving them but weeks later, in the middle of production.