Temperature Control for Bakeout

[Scott Schmucker]

Hi folks,

I'm looking for ways to improve bakeout control in our UHV lab and would be interested in knowing how everybody handles this necessary part of the job.  I'm seeking opinions on controllers for heater tapes or other ways to approach bakeout control in the UHV lab.

When baking our entire chamber, we use a hard-shell enclosure, which works great.  Where we don't have a good solution is baking ancillary plumbing or only a portion of the chamber (e.g. only the gas line).  These are systems with complex geometry that sometimes change; one would typically place a thermocouple and wrap a heater tape.  My primary goal is safety when the controller fails (we can't have things overheating or catching fire!), which has been a non-negligible challenge.  The second goal is to move away from manual temperature control; I hope to define my setpoint and walk away.

Here are some of the things I have done in the past:

(1) We've probably all used heater tapes and Variacs.  They work great, and tend to fail safely, but they require a lot of hands-on attention.  I'm hoping to find an alternative that includes more automated temperature control.

(2) I've also used the SDC series temperature controller from MDC (and other, similar products from other suppliers).  These have worked well until they fail.  The problem I've experienced is: when this setup fails the heater tape starts to smoke for reasons I don't fully understand (in principle the tape could plug directly into 120V AC and be within spec).  The same tapes on a Variac have never exhibited this problem.

(3) I've also used DMX controllers designed for theater lighting.  These are very convenient because they can be easily computer-controlled.  They fail infrequently, but when they fail they go to full power.  In theater lighting, I suppose this would turn the lights on to indicate a problem.  In a bakeout, this tends to overheat sensitive portions of the system.

With so many surface science labs running bakes, there must be alternative strategies I have not encountered.  I would appreciate if you were willing to share yours, and to share your experience with it.

Thanks,

Scott

[Jim Quinn]

Scott -

Get some cheap "eurotherms" or knockoffs.

I have never had problems with these.

Make sure the relay is normally open,

so they fail by shutting the circuit.

Don't cross your tapes.  Rule-of-thumb, keep one inch between spiral wraps.

Get a clamp-on ammeter to know your currents.

You can also purchase cheap PR10 power recorders.

- Jim

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[Kai HUANG]

Hi, Scott,

 

Perhaps you could check it up from hemi heating?

 

 

http://www.hemiheating.se/en/products/temperature-control/

 

 

Kai

Sent from Mail for Windows 10

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[Jonathan Shu]

Scott, 

A simple Eurotherm as someone suggested, works well, ramping is helpful too, as is RS232/485. I typically plug heating tape into variac into eurotherm, that way I know I can’t exceed a certain heat output. 

Thermocouple or RTD temperature input, I find RTDs to be more stable. With the Eurotherm, if the temperature input is lost, heat output shuts off. 

Jon

On May 1, 2020, at 12:36 PM, Scott Schmucker <scott.s...@gmail.com> wrote:



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[Randy D]

Hello Scott,

We designed our VB series bake out controllers to work with both IR lamps and heat tapes.   You can set the power like you do with a Variac, but there is also temperature feedback and a vacuum interlock so that the heaters will turn off when the chamber is out-gassing too much for the ion pumps or turbo pumps.  I use a BC-1 with an IRB600 and a heating tape on one of our in-house chambers almost every day and I really like how easy it is to bake out the chamber, and how well it works.

You can get more info at this link - https://rbdinstruments.com/products/water-vapor-desorption.html  

Randy