Re: Thermocouple mux 16 ch(4067) + A/D max187

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On 8 Dec 2005 08:22:30 -0800, "maxi" <maxitubo@xxxxxxxxxxx> wrote in message
<1134058950.500626.43440@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:

>i'm building a 16 ch nterface for reading 16 TC type K.
>I want switch the 16 TC only on positive wire and negative in common on
>ground with 74hc4067.
>Aftert the mux i place a AD595 and after a max 187 for reaDIN ON
>PARALLEL PORT on PC.
>Somebody has already made this?
>Do you think that is function?
>Any tips?
>
>Ciao,
>Massimo

Why do you want to "switch the 16 TC only on positive wire" ?

Conventionally one would use a two CD4067/4051's etc or a CD4052 to switch
_both_ leads of the thermocouples.  Typically this would be followed by an
amplifier. And one of the inputs would go to a temperature reference to
provide "ice point" reference.

But the AD595 (which I haven't used) incorporates amplification and ice
point, so you would seemingly just need to assure that the thermocouple
leads and the AD595 are at the same temperature but I don't know what the "
thermocouple failure alarm" circuitry consists in (that might be a
complication -- I don't know).

Or did I misunderstand your question?

Marc
Marc_F_Hult
www.ECOntrol.org