6.3 Setpoint guidance: ramp and synchronization

The set temperature you enter is the target. What the controller actually follows is an effective setpoint that approaches the target. Without any special setting the two are identical: the channel heats at the full permitted power until it arrives. Two functions deliberately hold the effective setpoint back.

Figure 18: The same set temperature, three ways of getting there. The ramp limits the gradient, the synchronization holds the channel back until the group has caught up.

Maximum heat-up and cool-down rate

The rate limits how fast the effective setpoint may change – stated in kelvin per minute, separately for heating up and cooling down. Both values are 0 ex works, that is switched off; the setpoint then follows every jump immediately.

What is limited is the setpoint, not the power. The channel therefore behaves as if somebody were slowly turning the setpoint up: at every instant it controls precisely, only towards a target that is still on its way. This is the difference from a power limit, see Section 6.8, “Power limits and power reduction” – that also makes heating up slower, but without the channel holding its temperature precisely while doing so.

What this is needed for:

Tools with walls of differing thickness crack at the transitions when heated up quickly. A limited heat-up rate keeps the temperature differences inside the part small.
Sensitive material in the channel does not tolerate a rapid change of temperature.
When cooling down the cool-down rate prevents a channel from cooling faster than the surrounding tool after standby or switch-off.

Heat-up synchronization

A tool consists of thermal zones of unequal mass. If all channels are switched on at the same time, the small nozzle is up to temperature after two minutes and the massive manifold after twenty. In the meantime the nozzle stands hot in a cold tool for twenty minutes – the material inside it decomposes, and the tool distorts.

Synchronization prevents this: the Thermonom continuously determines which channel of the group is furthest behind and limits the effective setpoints of the others to its temperature – with a headroom of about 3 K, so that the waiting channels do not come to a complete standstill. All channels therefore rise together and reach the set temperature at approximately the same time. Which channel is currently holding the group back is shown in the channel settings under “Limited by”.

Setting	Meaning
Master	This channel may hold the others back but waits for nobody itself. Useful for the zones with a large mass.
Slave	This channel waits for slower ones but holds nobody back itself.
Master and slave	Both. All channels wait for each other and arrive as simultaneously as possible. With very unequal zones this noticeably lengthens the heat-up time.
Off	The channel heats independently, as fast as it can.

Two conditions have to be met, otherwise nothing happens:

The channels have to be in the same group. Synchronization compares within one group, see Section 6.10, “Groups, substitution and failures”.
There has to be heating up. Only a rising target is synchronized. During standby and while cooling down nobody waits.

A channel counts as having arrived when it is less than 2 °C away from its set temperature. After that, synchronization is finished for this channel and it continues to control normally – a later drop at another channel does not hold it back again.

Why the two are mutually exclusive

Ramp and synchronization act at the same place: both write the effective setpoint. Two specifications for one value cannot be met at the same time – a ramp of 5 K/min and a group that permits 20 K/min would overwrite each other.

NOTE

If a maximum heat-up or cool-down rate is entered for a channel, it takes precedence. Heat-up synchronization then has no effect for this channel – even if it is set and the group is correct. If you want to synchronize, leave the rates at 0.