Multiple Thermistors

Projects General Guidance
1

Hi, I'm working on a project to monitor my barbecue smoker. It involves taking th measurement from two thermistors, one measuring food temp and one measuring the BBQ temp.

To measure the resistance of each thermistor, I place a known fixed resistor in series after each thermistor and read the voltage in between. Then I just use the voltage divider equation to calculate the resistance of the thermistor and hence temperature. This is repeated in both thermistors however it's important to note that the fixed resistor for each one each is appreciablely different.

The part that I forgot to think about is, since these thermistors and their cables are metallic if the cables of each touch one another or the grill then they short and whichever one had a larger fixed resistor will suddenly read incorrectly because the current is flowing to the other one through the path of least resistance. Does anyone have any suggestions how to get around this. I'll try to add a circuit diagram later to help facilitate the discussion.

2

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html

Are you using a "food grade" thermometer to measure food temperature?

Keep the leads apart.

Did you google high temp wire

Thanks... Tom...

3

Using a food grade thermistor is going to be your best option as suggested in the previous post.

You will also need to use thermistors that are completely sealed because even water and moisture will effect your readings if it's getting between the two leads.

4

I am using two separate food grade thermistors. My problem is even the cabling that runs off of the thermistors is braided metallic cable (it is that way due to the high temp). The issue is, if the cabling of the thermistors comes into contact with one another or both touch the grill - then they short one another.

5

Hi,
Can you post a picture of your thermistors and their leads please?

Thanks.. Tom.. :slight_smile:

6

The food grade thermistors that I'm using have an outer steel braided shield but the other conductor is just a high temp wire running down the centre of the shield.

If this is the case with yours then just connect the braided shields on each to ground or V+ (preferably ground) and your shorting issues will be gone.