[time-nuts] Low CostTemperature sensor

[Tom Miller]

I agree with both of you. I can't imagine using the reverse leakage of a 
diode to measure temperature without some difficult and expensive design. 
Also, the transistor is using the forward biased B-E diode against what he 
stated in the article.

And sloppy would be the best description.

Thanks guys. Glad I am not the only one forming that opinion.

Regards,
Tom


----- Original Message ----- 
From: "Scott Stobbe" <scott.j.stobbe at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Tuesday, January 17, 2017 9:10 AM
Subject: Re: [time-nuts] Low CostTemperature sensor


> Thermometry based on Diode leakage current wouldn't be impossible I
> suppose, you might loose some hair in the process.
>
> The signal levels on the opamp are goofed too.
>
> On Tue, Jan 17, 2017 at 4:19 AM Charles Steinmetz <csteinmetz at yandex.com>
> wrote:
>
>> Tom wrote:
>>
>>
>>
>> > That article has a major error. Anyone know what it is?
>>
>>
>>
>> Well, the author says the reverse current of a diode is "directly"
>>
>> proportional to temperature.  This could suggest that he means the
>>
>> relationship is linear (the relationship is actually exponential with
>>
>> absolute temperature).  But that's not really an *error* -- just sloppy.
>>
>>   "Direct" does not necessarily imply "linear."  An exponential
>>
>> relationship is "direct" in the sense that it is what mathematicians
>>
>> call "injective" (every temperature corresponds to exactly one value of
>>
>> reverse current).
>>
>>
>>
>> Then, in discussing the LM95235, he says that it can use the
>>
>> "collector-emitter junction diode" of a transistor as the sense element.
>>
>>   Of course, a bipolar transistor has no collector-emitter junction.
>>
>> His diagram correctly shows a diode-connected NPN operating in the
>>
>> active region (forward biased, not reverse biased as the rest of his
>>
>> article discusses) as the sensor for the LM95235.
>>
>>
>>
>> Are any of these what you had in mind, or is there more?
>>
>>
>>
>> Charles
>>
>>
>>
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