The Secret Society of Lathe Trolls

blacknwhite · Joined: 24 Apr 2008 Posts: 271 Location: US

QUESTION: Monitoring head coil temperature:

How is it done?

I've heard people mention, "...he drove the cutterhead coil up to N degrees celsius..." Is there an actual temperature sensor on some brands of heads?

Or, is there really no such thing as temperature sensors on cutterhead drive coils, and some good cutting amps just show an "estimated temperature" based on the strength of electircal signal being fed to the cutterhead?

If that's the case, what aspect exactly of the signal correlates to temperature? Current? velocity?

- Bob

markrob · Joined: 28 Nov 2007 Posts: 157 Location: Philadelphia Area

Hi Bob,

I have a JAES paper on the subject titled "Essential Equipment for the Transmission of High Peak Levels in the Disk-Cutting System SAL 74/SX 74" by Kern and Weiss of Neumann. The head temp is measured by using the tempco of the wire in the voice coil. They indicate that at 20 C, the resistance of an SX74 is 4.7 ohms rising to 8.2 ohms at 200 C. They use a freq compensated bridge circuit with the coil as one of the lower legs. The power amp drives the top of the bridge the balance is monitored in real time.

blacknwhite · Joined: 24 Apr 2008 Posts: 271 Location: US

Thanks Markrob! - found it - volume 1, page 277 - I need to go back and skim all the articles I passed over on the first reading.

- Bob

markrob · Joined: 28 Nov 2007 Posts: 157 Location: Philadelphia Area

Hi Bob,

I just got my copies of the JAES reprints. There is so much stuff in there, I think it'll keep me busy for quite a long time Laughing