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Ping Tim Wescott

Yo, Tim!

I'm licensing a very low noise laser controller to a customer. They'll be using it with combined laser/TEC modules of their own design, and so they need to be able to tune the temperature control loop. It would be good if that were done by changing fixed RC values rather than pots.

Do you have any suggestions for software tools I could point them to, that would tell them where to put the poles and zeros?

Failing that I'll just write them one, but it would be a bit of a pain.

Thanks

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
https://hobbs-eo.com
Reply to
Phil Hobbs
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What's the input? Open loop step/ pulse response?

I made a pid loop pcb with terminal blocks for the R's.

George H.

Reply to
George Herold

The input is a control voltage from 0 to 10V, corresponding to 0 to 50 C.

I usually do the compensation using the delay plus integrator model--you stick a current step into the TEC and watch the response at the temperature readout. At early times it looks like a time delay followed by a ramp.

The model is

H_plant(f) = A exp(j 2 pi f t_delay) / (j 2 pi f tau)

where tau is the integrator time constant.

Then you apply a PI loop, generally just an op amp integrator with a resistor in series with the integration cap:

H_amp(f) = (1 + j 2 pi f tau_zero) /j 2 pi f tau_int

You can solve this analytically to a reasonable approximation, given the desired phase margin, but it isn't clear that the customer can easily handle that even if I give them the expression--they're smart people, but mainly MEs and biomeds.

Besides, we haven't heard from Tim Wescott in months, so it was a good excuse. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
https://hobbs-eo.com
Reply to
Phil Hobbs

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