DS18B20 alternative

[Mark.R]

Hi all its been a while since I've posted or commented on anything on here but have to say as always reading through other posts I usually find the answer to my problems.

This post is just a general question to pick your brains. Recently I've been reading a bit about these 1-wire temp sensors and am thinking of replacing some thermistors in a project with them.
My question is (get there in the end) is do any of you know if a high temp version of the DS18B20 exists, I see these go to 125C but could do with one that is happy to sit at 150 or maybe 200C.

Any thoughts much appreciated.

Mark

 

[MPep]

You'll probably need to start looking at thermocouples. Various examples on this forum.

 

[premelec]

A lot depends on distance of leads and accuracy / stability - there are a few thermistors good for about 300C and platinum units could work - thermocouples have their place in high temperature measurement with some complications - take a look into these and see if any suit your needs and level accuracy & signal conditioning... they aren't as straightforward as the DS18B20... [non contact IR sensing is good for some situations... ]

 

[John West]

While certain power semiconductors may be designed to handle those temperatures, I've not seen any integrated semiconductors rated to do so. Those temperatures get you into the realm of specialized, low production-volume devices, so you're not likely to find a DS18B20 type device that meets those specs at anything like an affordable price, if one is made at all.

 

[Mark.R]

Ok, thank you for the replies.

 

[the old fart]

I once used a 'max6675' chip and thermocouple to control a model boat steam boiler.

 

[Mark.R]

Sounds interesting, do you have any more detail on what you did at the time?

 

[westaust55]

Sounds interesting, do you have any more detail on what you did at the time?

@Mark,

Try a search of the PICAXE forum using "max6675" as the search parameter.
I came up with 27 hits in threads where people sought help or provided assistance.
It may save you waiting for others to respond to your question if they do not immediately have the answer/information to hand.

 

[the old fart]

Sounds interesting, do you have any more detail on what you did at the time?

Hi Mark,

; Picaxe 20X2 to Max6675 thermocouple
setfreq m8
Symbol CS = B.6           ' connect pin12 to pin 6 MAX6675
Symbol SCK = B.7          ' connect pin11 to pin 5 MAX6675
Symbol MISO = C.1 ' connect pin9  to pin 7 MAX6675
symbol baud=n2400
Symbol Val = W0
Symbol Digs = B4
Symbol I = B5
Symbol J = B6
low sck
high cs
init: pause 500

       serout B.0,baud,(254,1)
       pause 30

Main:



MeasTemp:

Val = 0
    Low CS   ; stop conversion
pause 10
     For i =0 to 15   ' serial clock in 16 bits
        High SCK  ; clock high
	    val=val*2+pinc.1	
	  Low SCK ;  clock low
	Next I
     High CS		' deselect the 6675 finish transfer
Val = Val / 32     ' use only the 11 most sig bits
w10=w10+val/2
   serout b.0,baud,(254,212,"Temp=",#w10,"  ")

 goto meastemp

Rough program that I put together yesterday, from existing programs posted on this forum.
I would use the reading from W10 to control a servo which adjusts the gas flow to the boiler.

Remember to add the '104' capacitor across pins 1&4 of the max6675 chip, makes a stable reading.

TOF

 

[Mark.R]

Thanks for taking the time to reply its a big help.

 

[Mark.R]

Hi me again. I've finally got round to doing some more with this but have hit a problem. I'm using the following code in an 08M2+ linked to the MAX6675 and all it displays serial terminal is Temp=0

Any ideas?

View attachment Thermocuple.bas

 

[premelec]

Probably need to see your circuit...