Subject: Thermister in CCD head box
From: Alan Stummer <astummer_at_physics.utoronto.ca>
To: Robin Marjoribanks <marj_at_physics.utoronto.ca>
Date: Thu, 24 May 2007 09:51:38 -0400

Hi Robin;

OVERVIEW:  For the record, this is a description of the thermistor 
inside the EEV CCD head box.  It is 1K at 25°, NTC (negative temperature 
coefficient), Panasonic ERT-D2FGL102S 
(http://www.panasonic.com/industrial/components/pdf/arg0000ce2.pdf, 
PNT113-ND at www.digikey.ca).  It is floating, connected to two spare 
terminals on the connector between the head board and the head box, 
terminated with a BNC.

CONNECTIONS:  See attached pic.  Direct  resistance measurement across 
the BNC should show about 1K Ohm.  Pressure measurement is done by 
dissipating about 1/4W from the thermistor and measuring its 
temperature:  air provides convection cooling.  Using a 15VDC/50mA 
supply, put 200Ohms/0.5W resistor in series with +ve.  Connect this 
resistor to BNC (prefer centre pin), connect 15V -ve to BNC (prefer 
outer pin).  Use a BNC-tee to measure the voltage at the BNC.

TO MEASURE PRESSURE:  With 1 bar ambient pressure, turn on 15V supply, 
allow several minutes for the thermistor to stabilize, measure the 
voltage; it should be about 7.2V.  Pump down the chamber.  If the box 
looses pressure, the thermister will heat and the voltage drop to about 
6.2V.

MEASURED VALUES (head box open to vacuum):
1 bar: 7.20V
80 torr: 6.93V
0.1 torr: 6.15V

Cheers,
Alan

-- 
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Alan Stummer
University of Toronto - Physics
Quantum Optics Labs
416-978-4400
www.physics.utoronto.ca/~astummer
Skype: alan.stummer
Google IM: alanstummer
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