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Entry  Mon Aug 28 16:19:53 2017, Kira, Summary, TempCtrl, temp sensor TempSenseFront.jpgTempSenseBack.jpgIMG_20170814_121758~2.jpgIMG_20170821_124429~2.jpg
    Reply  Mon Aug 28 22:30:34 2017, Craig, awade, DailyProgress, TempCtrl, temp sensor TempSenseWithLowPassFront.jpgTempSenseWIthLowPassBack.jpgLowPassSchematic.jpg
Message ID: 1884     Entry time: Mon Aug 28 22:30:34 2017     In reply to: 1883
Author: Craig, awade 
Type: DailyProgress 
Category: TempCtrl 
Subject: temp sensor 

Kira built the circuit below and and handed it off to Andrew and I at around noon today.  We tested it and found it was extremely noisy.  Andrew stuck a passive low pass filter on it and the circuit immediately calmed down and gave steady output.

I took Kira's circuit and soldered on an active low pass filter with an OP27.  The resistor is 10kΩ and capacitor is 22µF, so the corner frequency of the low pass is around 0.35 Hz. 

Hopefully this will calm down the temperature voltage monitor output of the circuit, and we can have at least an idea of the temperature fluctuations of our can.

Quote:

I built a temperature sensor prototype for the 40m lab, which can be used for the PSL lab as well for temperature stabilization. It consists of an AD586 5V constant voltage output, an AD590 temperature sensor (I initially had 592 but they are very similar), and a LT1012 OP amp, along with a 10K resistor and a few capacitors (see first schematic). It uses the temperature of an object that touches the AD590, which is attached to a long cable, and converts it into a current (1microA/K), which is converted by the OP amp and resistor into a voltage. The AD586 is required because the sensor wants a constant input of 5V to accurately measure temperature. I used a 10K resistor on the OP amp so that the voltage should be around 3V when measuring room temperature. It requires an input of +15V and -15V to the OP amp, 15V to the input of the AD586 (this is shared with the +15V input to the OP amp), and a ground. The +15V (red) and -15V (black) inputs are given to the pins closer to LT1012 and the ground is farther away. The output voltage is read out through a BNC cable and can be converted into a temperature in K by multiplying the value by 100, but it shows a temerature that is about 2K higher than the actual temperature.

In addition, I used capacitors on the OP amp to stabilize the voltage input. I used a 100nF ceramic capacitor placed close to the pins of the OP amp and a 100microF electrolytic capacitor placed father away to achieve this. I have attached the schematic for this as well (second schematic), with 1 being the electrolytic capacitor and 2 being the ceramic capacitor.

 

Attachment 1: TempSenseWithLowPassFront.jpg  2.256 MB  | Hide | Hide all
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Attachment 2: TempSenseWIthLowPassBack.jpg  2.339 MB  | Hide | Hide all
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Attachment 3: LowPassSchematic.jpg  1.323 MB  | Hide | Hide all
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