Thermocouple for prepregs

What thermocouple do you guys recommend for oven curing prepregs? I’ve seen some setups with multiple leads in direct contact with the parts.

I tend to prefer not having anything in direct contact with the parts as it can mess with the ramp rates of the oven. Composite tools can have a big delay in heating up, so the oven cranks the heat up because it thinks it isn’t hot enough, then when the tool temp catches up you end up way over temperature and potentially beyond your tools Tg. In my experience it is better to combat the lag in the tool temperature with slower ramp rates and longer soak durations, so it tends to come down to working out what works with your specific moulds.

I do however occasionally use an external thermocouple on or near the tool just to monitor the temperature there rather than control it. I normally do this when trying to troubleshoot any flaws I’m getting, sometimes a new mould wants a slightly different cure cycle to other moulds to give perfect results. It’s more just about knowing what is going on so you can make changes.