Nadcap HT - Furnace Instrumentation Type - Control Zone definition

[juhav]

We have a 20 years old Smitz&Apelt drop bottom furnace which should be upgraded to fulfill AMS2750D requirements in instr.type C. Now we have 8 control sensors to record temperatures. There is also 8 heat elements and 8 fans that are controlled separately.

In AMS2750 par. 3.3.1.3.3 it states that at least two additional recording sensors in each control zone shall be located to best represent the coldest and hottest temperatures based on the results of last TUS. We are struggling with the term Control Zone. In par 8.2.10 AMS2750 states that Control Zone is a portion of the working zone having a separate sensor/instrument/heat input mechanism to control its temperature.

Does this mean that we do really have 8 control zones so we will have to add total of 16 new sensors to record highest/lowest temperatures from each control zone. Or as we would like to understand, we shall place total of two new sensors to measure and record highest and lowest temperatures inside working area. With those 8 separate controllers we are trying to reach maximum temperature uniformity, not give different parameters to each part of furnace.

Can someone please clarify this, thanks...

 

[Stijloor]

Any heat treat experts that can help?

Thank you!!

Stijloor.

 

[BradM]

We have a 20 years old Smitz&Apelt drop bottom furnace which should be upgraded to fulfill AMS2750D requirements in instr.type C. Now we have 8 control sensors to record temperatures. There is also 8 heat elements and 8 fans that are controlled separately.

In AMS2750 par. 3.3.1.3.3 it states that at least two additional recording sensors in each control zone shall be located to best represent the coldest and hottest temperatures based on the results of last TUS. We are struggling with the term Control Zone. In par 8.2.10 AMS2750 states that Control Zone is a portion of the working zone having a separate sensor/instrument/heat input mechanism to control its temperature.

Does this mean that we do really have 8 control zones so we will have to add total of 16 new sensors to record highest/lowest temperatures from each control zone. Or as we would like to understand, we shall place total of two new sensors to measure and record highest and lowest temperatures inside working area. With those 8 separate controllers we are trying to reach maximum temperature uniformity, not give different parameters to each part of furnace.

Can someone please clarify this, thanks...

Hello there! I certainly am no expert by any means, but I'll give it a try.

To clarify: monitor/recording zones are different than control zone. When it is referring to control zone, that is how many temperature sensors are used to adjust the control temperature.

Do you have one burner (or heating bank) with one set of controls? Then that is one zone. That regulates the temperature throughout the working zone. If you have two heat sources (Zone A and Zone B), typical of larger ovens, then you would have two zones, and so forth.

Also, if you have a large furnace and your uniformity survey are done in different zones (due to maximum thermocouples), then you would need the min/max for each of those zones.

I have a hard time envisioning that the furnace would have 8 independent control zones. Are there 8 separate temperature controllers? Why so many? Can you map the furnace with one TUS? If so, and you can demonstrate adequate control over the controllers (locked PID; probes aren't moved; etc.) I would think you could ask your auditor to allow two probes in hot/cold based on the survey results.