best sensors...

Discussion of the physical aspects
User avatar
rspiger
Posts: 14
Joined: Sun Sep 09, 2012 9:24 am
Bot?: No

Re: best sensors...

Post by rspiger »

That is excatly what i was looking for in a probe a disconnect. I was thinking abbout trying to place a GM weather pack connecter in line and see if it changed the impedance or resistance of the cable.

But if youor tooling up to make these I'll take four?
Blasted Bassett Brewery
User avatar
bbrally
Posts: 210
Joined: Sat Mar 27, 2010 3:59 am
Bot?: No
Location: Vancouver, BC
Contact:

Re: best sensors...

Post by bbrally »

There was nothing wrong with my previous fermentor tri-clamp probe, but since I was redoing the brewery I thought I might as well put my last connector to use.

Thanks for the complements guys. I'd be happy to make these up for little more than the cost to me, but getting all the parts shipped ($) to me and then waiting to have time to assemble could take a while. Would people be willing to pay $50 each including a dozen feet of sheilded wire with connector?
Fermentor probe....just because I could.
Fermentor probe....just because I could.
IMG_0840.JPG (40.65 KiB) Viewed 6477 times
clearwaterbrewer
Posts: 383
Joined: Wed Feb 09, 2011 3:43 pm
Bot?: No
Location: Clearwater, FL
Contact:

Re: best sensors...

Post by clearwaterbrewer »

nice job! Thanks for posting where you got the M8 connectors, I like those!

now I am thinking... I could weld a inside threaded sleeve to the probe so it screwed on to the receptacle, and use a spring clip of some sort to hold the thermistor against the inside tip of the probe, but can be removed if needed..
User avatar
bbrally
Posts: 210
Joined: Sat Mar 27, 2010 3:59 am
Bot?: No
Location: Vancouver, BC
Contact:

Re: best sensors...

Post by bbrally »

I like the idea of the spring clip.

A little heat will soften the epoxy bond of the receptacle to the probe enabling removal, but the sensor would probably be destroyed if I were to try and remove it for some reason.

I looked at the sensors and found out that digikey sent me MF51E103E3950 which are 0.5% tolerance instead of the 1.0% cheaper ones I'd ordered. When I entered the proper coeffieicients into the BCS, all my temps were within 0.1°of each other. Most were equal. That's a far cry from the 2-3° difference I got when using cheap Chinese thermistors.
Rick
Posts: 14
Joined: Fri Jan 25, 2013 8:21 am
Bot?: No

Re: best sensors...

Post by Rick »

bbrally I am shamelessly ripping off your idea for the M8 connecting probes, thanks! I copied and pasted your part number for the thermisters and ordered them from DigiKey. I just got them in and the do say they are +-.5%, NTC, but they also say 3950K. I have no idea how these things are rated, but I thought we were supposed to use 10Ks? I'm assuming they work fine for you and will for me. Also, for the eternal gratitude of someone you will never meet, could you share your coefficients for these thermisters?
User avatar
bbrally
Posts: 210
Joined: Sat Mar 27, 2010 3:59 am
Bot?: No
Location: Vancouver, BC
Contact:

Re: best sensors...

Post by bbrally »

Here's the numbers I've used:

A: 0.0011252569
B: 2.3538846E-4
C: 7.72545E-8

Here's the address of the resistance - temperature (R-T) chart for these thermistors: http://www.cantherm.com/products/thermi ... stics.html

The top of that page gives a definition of where the 3950K comes from. It's over my head, but I understand it as follows.

This number is called the beta value and the 'K' refers to degrees Kelvin, not thousands of ohms. The beta value is used to express the R-T relationship just as the three Steinhart–Hart coefficients do, but not as accurately.

This company makes four different 10K ohm thermistors. All would work, but as can be seen in the chart, the spread of the resistance increases with a higher beta number, so different coefficients would be required for the four different thermistors. All four 10K thermistors have a resistance of 10K at 25 deg C., but resistance between the four varies outside of this temperature.

The +-.5% refers to how closely the thermistor matched the R-T chart. So a lower number will give less variance in temperature readings among different thermistors. You could get accurate temp readings from 10% thermistors if you were to calibrate each one individually and enter their unique SH coeffiecients. But for a small premium in price, these thermistors can all use the same SH coeffiecients and still be very accurate without the hassles of calibration.
Rick
Posts: 14
Joined: Fri Jan 25, 2013 8:21 am
Bot?: No

Re: best sensors...

Post by Rick »

Excellent! My M8 connectors should be here today and I'll start putting these together. I found a US source for the chassis plug and a right angle connector with 5 meter pigtails. They were quite a bit cheaper, hope they work. I appreciate you taking the time to write up all the info. I must have missed the link to the details on these thermisters, thanks for that as well.
lewdog50
Posts: 14
Joined: Wed Feb 26, 2014 3:28 am
Bot?: No

Re: best sensors...

Post by lewdog50 »

What is the link to the US source for the M8 connectors?
Post Reply