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Message ID: 1331     Entry time: Sun Feb 22 23:43:07 2009
Author: caryn 
Type: Summary 
Category: General 
Subject: temperature sensor 


So, to compare temp channels, I made a plot of PSL-FSS_RMTEMP and PEM-MC1_TEMPS(the test temp sensor channel after converting from cts to degC). This plot begins about 2 months ago t_initial=911805130. The temperature channels look kinda similar but MC1-TEMPS (the temp sensor clamped to MC1,3 chamber) is consistently higher in temperature than FSS_RMTEMP. See compare_temperature_channels.png.

MC1-TEMPS isn't exactly consistent with FSS-RMTEMP. I attached a few plots where I've zoomed in on a few hours or a few days. See compare_temperature_channels_zoom1.pdf & compare_temperature_channels_zoom2.pdf

Change the room temperature, see what happens to the chamber temperature

A while ago, somebody was fiddling around with the room temperature.  See compare_temperature_channels_zoom4.pdf.  This is a plot of PEM-MC1_TEMPS and PSL-FSS_RMTEMP at t0=911805130. You can see the chamber heating up and cooling down in happy-capacitory-fashion. Although, the PSL-FSS_RMTEMP and the PEM-MC1_TEMPS don't really line up so well. Maybe, the air in the location of the MC1,3 chamber is just warmer than the air in the PSL or maybe there's an offset in my calibration equation.

Calibration equation for PEM-MC1-TEMPS

For the calibration (cts to degC) I used the following equation based on the data-sheet for the LM34 and some measurements of the circuit:


How does the chamber temperature compare with the air temperature?

It looks like the chamber may be warmer than the air around it sometimes.

I wanted to check the temperature of the air and compare it with the temperature the sensor had been measuring. So, at t=918855087 gps, I took the temp sensor off of the mc1-mc3 chamber and let it hang freely, close to the chamber but not touching anything. See compare_temperature_chamber_air.png. MC1_TEMPS increases in temperature when I am handling the temp-sensor and then cools down to below the chamber temperature, close to FSS_RMTEMP, indicating the air temperature was less than the chamber temperature.

 When, I reattached temp sensor to the chamber at t=919011131 gps, the the temperature of the chamber was again higher than the temperature of the air. See compare_temperature_air2chamber.pdf.

Also, as one might expect, when the temp-sensor is clamped to the chamber, the temperature varies less, & when it's detached from the chamber, the temperature varies more. See compare_temperature_air_1day.pdf & compare_temperature_chamber_1day.pdf.

New temp-sensor power supply vs old temp-sensor power supply

The new temp-sensor is less noisy and seems to work OK. It's not completely consistent with PSL-FSS_RMTEMP, but neither was the old temp-sensor. And even the air just outside the chamber isn't the same temperature as the chamber. So, the channels shouldn't line up perfectly anyways.

I unplugged the 'old' temp-sensor power supply for a few hours and plugged in the 'new' one, which doesn't have a box but has some capacitors and and 2 more voltage regulators. The MC1_TEMPS channel became less noisy. See noisetime.png & noisefreq.pdf. For that time, the minute trend shows that with the old temp-sensor power supply the temp sensor varies +/-30cts and with the new power supply, it is more like +/-5cts (and Volt/16,384cts * 1degF/10mV -->  apprx +/-0.03degF). So, it's less noisy. 

I kept the new temp-sensor power supply plugged in for about 8 hours, checking if new temp sensor power supply worked ok. Compared it with PSL-FSS_RMTEMP after applying an approximate calibration equation. See ver2_mc1_rmtemp_8hr_appxcal.png.

Just for kicks

Measuring time constant of temp sensor when detached from chamber. At 918858981, I heated up the temp sensor on of the mc1-mc3 chamber with my hand. Took hand off sensor at  918859253 and let it cool down to the room temperature. See temperature_sensor_tau.pdf. 

Attachment 1: compare_temperature_channels.png  10 kB  | Hide | Hide all
Attachment 2: compare_temperature_channels_zoom1.pdf  10 kB  | Hide | Hide all
Attachment 3: compare_temperature_channels_zoom2.pdf  11 kB  | Hide | Hide all
Attachment 4: compare_temperature_channels_zoom4.pdf  6 kB  | Hide | Hide all
Attachment 5: compare_temperature_chamber_air.png  10 kB  | Hide | Hide all
Attachment 6: compare_temperature_air2chamber.pdf  7 kB  | Hide | Hide all
Attachment 7: compare_temperature_air_1day.pdf  9 kB  | Hide | Hide all
Attachment 8: compare_temperature_chamber_1day.pdf  7 kB  | Hide | Hide all
Attachment 9: noisetime.pdf  14 kB  | Hide | Hide all
Attachment 10: noisefreq.pdf  15 kB  | Hide | Hide all
Attachment 11: ver2_mc1_rmtemp_8hr_appxcal.pdf  6 kB  | Hide | Hide all
Attachment 12: temperature_sensor_tau.pdf  5 kB  | Hide | Hide all
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