# Celsius zero shift for two -terminal temperature sensor circuit not completely understood?

#### TarikElec

Joined Oct 17, 2019
125
Hi everyone,
So, as I am reading this part of amazing book, the Celsius zero shift for two -terminal temperature sensor circuit of Fig 21.19 is not fully understood by me.
what I understood:
-The $V_{\text{Temp}}$ at the two terminal of the Zenner diode is directly coming from the circuit Fig.21.18 which is the output is of value (10mV/K)*T
-the current frlowing through the V-(not in) is the sum of Vo/10Kohm+Vref/9.16Kohm.
-the only time I get the Vo=-2.73V is when the $V_{\text{Temp}}=0$ and a that value the current flowing through the V-(not in) is negligible.
What I did not understand:
1-where did the formula come from, it is like converting Kelvin to Celsius? $V_{\text{o}}=\left(\frac{10\text{mV}}{\text{Celsius}}\right) v$
2-what does the $v$ stand for?
3-at C=0, it means Tk=273Kelvin and then V_temp=10*273=2.73V which bring the Vo~=0V?

here , is the page of the book and falstad simulator:

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#### crutschow

Joined Mar 14, 2008
34,689
where did the formula come from, it is like converting Kelvin to Celsius?
Do you know that degrees Celsius is just degrees Kelvin plus 273.15?

#### TarikElec

Joined Oct 17, 2019
125
Do you know that degrees Celsius is just degrees Kelvin plus 273.15?
Zes I know that it is the other way around: Tk=Tc+273.15. but that does not answer my question of if the voltage across the zenner diode is the Vtemp of the fig 21.18 for example

I think I understood it. the circuit in Fig 21.19 is just the Tc=Tk-273 and the the -273uA flowing to the R=10Kohm of the Vo is just this reflection of 10Kohm*(-273K) at Tc=0(0=Tk-273K).
the 273uA comes from the Vref/9.16 Kohm that flows through the 10Kohm of Vo as Vtemp=0V at Tk=0 where no current flows via the 10Kohm connected to the zener diode
but at Tk=273,Tc=0, we have Vtemp=2.73V and this leads to Vo=0

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#### Casperson

Joined Aug 11, 2021
4
Your temperature sensor is not a zener diode, it's an integrated circuit that is connected like a zener diode and has a voltage drop of 10 mV per K,

Note: K is only called Kelvin, not degree Kelvin, because it is an absolute temperature and not a relative temperature like degree Celsius, degree Fahrenheit or degree Réaumur (degree means relative scale).