Thursday, March 20, 2014

Followup on hot camera

Did some work on the camera without spending money.  As noted earlier, I had some Arctic Silver compound in my kit from other projects.  I removed all of the old compound, including the most recently applied material and used the Arctic Silver in its place.  This material is supposed to be the bee's knees, even though it has a long set time (200 hours).

I also put a terminal block on the heatsink baseplate to facilitate changing parts. 

I put the Tellurex C2-30-1503 in place of the larger wattage device.  The drop of 10 watts should help control the generation of unwanted heat.  Since I'm driving the device at full Voltage with no modulation, there seems to be a lot of waste heat with a larger device.  A nice advantage is that the current use drops by a full amp.

While I had the camera apart for the Arctic Silver exercise, I looked deep inside the guts.  I could see where the sensor assembly floats and moves.  With looking at the way stuff fits inside the path, I cut a small pad of the thermal gel and slipped it inside the cavity.  I did not remove the cling plastic as I wanted to be able to have it slip inside the camera without snags.  Learned a few things about the way the sensor plate moves when the camera takes a picture.  I'd assumed that the resting point for the sensor plate was "neutral" and that when the camera takes a picture with the shake reduction turned off, it would not need to float.  After I put the thermal pad in place, I noticed the way the plate moves.  The sensor floats free when unpowered and then as the camera takes the picture, the sensor "unparks" to approach the proper distance and location.  Even with the shake reduction turned off, the sensor must move.  Very interesting!

With testing after this addition of the thermal pad covering part of the back of the sensor, I checked some darks.  I was pleased to see that the relative darkness of these new images is notable.  Yes, amp glow still reigns in the same place.  However, the standard deviation of noise in the central section drops from 13 to 12 when at 19C.  I'll check other temperatures as I can.

After a few hours of running the camera on the desktop, I'm a little annoyed that the EXIF temps hold at 19-20C.  There's no real movement to a lower setpoint.  The standard deviation on the dark frame shows the same range - 13 to 15.  Interesting to note that the hot pixel library in Maxim is still leaving a few stragglers, may be what's causing the high numbers relative to the old examples.  Std Dev of the bias signal is 1.096.  Tomorrow I'll put the camera in the fridge and see what happens vs the desktop.  If the results don't show much additional promise, then I think I'll need to look at stacking devices for a trial.  I have several to try.  I can rig in parallel to see what happens. 

I did some math on what to expect with the stacked peltier/TEC devices.  I have decided to stack the C2-30-1505 on top of the 1503 device.  Based on the numbers that I have for the current use and Qc at this current, it should work.  The question becomes whether the heat sink will be up to the task of removing the waste heat.  If it's not, then the experiment moves towards water cooling.

At this time, the old thermocouple sensor wires are still hanging out of the camera.  I'd like to find a way to use this available data.  I have found the resistance to C chart for the probe.  I could just use the multimeter to see how it performs.  Unfortunately, I did not pay attention to where the probe ended up during the last assembly.  It may be loose and not contacting anything of interest.
From http://www.mcshaneinc.com/html/TS67_Specs.html?NewWin#CurveCoefficients

A final step that I did to combat the rotation problem at the TMount, I put a few dabs of hot melt glue in the seam and gap from where the locking pin goes.  I can remove this glue with just picking at it with my fingernail if I must change it.  Otherwise, it seems to hold the bayonet adapter nice and firm.  Should have done this long ago!