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Entry  Wed Aug 16 16:05:53 2017, Kira, Update, PEM, temp sensor PCB IMG_20170816_154514.jpgIMG_20170816_154541.jpg
    Reply  Thu Aug 17 10:41:58 2017, Kira, Update, PEM, temp sensor PCB IMG_20170817_095917.jpg
       Reply  Mon Aug 21 13:07:08 2017, Kira, Update, PEM, temp sensor PCB IMG_20170821_124121.jpgIMG_20170821_124429~2.jpgIMG_20170821_124108.jpg
Message ID: 13232     Entry time: Mon Aug 21 13:07:08 2017     In reply to: 13224
Author: Kira 
Type: Update 
Category: PEM 
Subject: temp sensor PCB 

On Friday, I cleaned up the circuit so that there are only three connections needed (+15V, -15V, GND) and a BNC connector for reading the output. Today, I added in bypass capacitors. The small yellow ones are 0.1 microF ceramic, and the large ones are 100 microF electrolytic. They are used to stabilize the +15V and -15V inputs to the OP amp and minimize fluctuations, since it doesn't have a regulator for stability. I have also attached the circuit diagram for the OP amp only, where 1 are the electrolytic and 2 are the ceramic. The temperature is still about 2 degrees off, but if that difference is constant for all temperatures in our range we can just calibrate it later.

Here is a helpful link on bypass capacitors (thanks to Kevin for sending it to me).

As a note, the electrolytic capacitors do have a polarity, so it is important to place them correctly (the negative side is towards the lower voltage potential, and not always towards ground).

Quote:

Got it to work. One of the connections was faulty. I decided to check the temperature measured against a thermometer. The sensor showed 26.1 C, but the thermometer showed 25.8 C after I let them both cool down after heating them up. The temperature of the thermometer was dropping at the time of measurement, but the temperature of the sensor was not. This is still a rough version of the final sensor, so I'm not sure what exactly causes this discrepancy.

Quote:

Tried taking the circuit from the breadboard to the PCB. I attached all the components to adapters that would allow them to be connected to the PCB. From the first picture, the first component is AD586, the second is AD590, and the third is LT1012, along with a resistor across it. I then soldered the connections between the components, as can be seen in the second picture. When I tested out this version of the circuit by hooking it up to the DC source, I got a reading of ~-15V. I will have to check all the connections to make sure there is contact where there should be one, and no contact where there shouldn't be. I had issues attaching the tiny AD590 and LT1012 to its adaptor, so the issue may lie there as well. I'll also check that each component is in working order as well.

Once I figure out where my error is, my plan is to build two more of these and place a metal object such that it contacts only the surface of the AD590s. This would allow me to compare the three values to the actual temperature of the metal, which would then tell me how accurate this setup is.

Note on the resistor: I measured all the resistors and chose three that had exactly 10.00k Ohm. The voltage detected is dependent on the resistor, so if we are to take three identical copies, I ensured that there would be no error due to the resistors being a little different.

 

 

Attachment 1: IMG_20170821_124121.jpg  3.365 MB  | Show | Show all
Attachment 2: IMG_20170821_124429~2.jpg  393 kB  | Show | Show all
Attachment 3: IMG_20170821_124108.jpg  3.000 MB  | Show | Show all
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