KrNews #09 18 мая 1999

Железо

Ferrum! - An attachment for measuring the temperature of a digital multimeter.

(C) Mr.Linker



  Attachment for measuring the temperature
DMMs


  Easy attachment containing six
resistor allows the use of a digital voltmeter to measure the 
temperature with a resolution of 0.1 degrees and

thermal inertia of 10 ... 15 seconds. When
such a speed it can be applied
and to measure body temperature. In the measuring device to 
make changes not required, and production consoles available 
for beginners and amateurs. 

  As the sensor is applied Semiconductor thermistor ST3-19 with 
a nominal resistance of 10K at T = 20 degrees.

 Together with an additional resistor R3
He forms one half of the measuring
bridge. Second half - a voltage divider of resistors R4 and R5, 
the last calibration sets the initial

the output voltage. Multimeter is used in the measurement mode
constant voltage on the 200
or 2000 mV. Appropriate choice
resistor R2 change
sensitivity of the measuring bridge.

  Immediately before measuring the temperature variable 
resistor R1 sets the supply voltage measuring circuit equal to 
that at MDM performed the initial calibration.

Include the prefix for the reference temperature measured by 
push-button switch SB1, and the translation of the measurement 
mode, setting mode voltage - switch SB2.  Calibration consoles 
produced in two points:


 TM TK1 = +0.707 (T2-T1) / 2
 Tk2 = Tm-0.707 (T2-T1) / 2

where: TM = (T1 + T2) / 2

    T1 - the beginning of the temperature range

    T2 - The End of the temperature range


  During the initial calibration
with a fresh power cell resistance of the variable resistor R1 
sets the maximum, to the extent of loss capacitance and voltage 
reduction element it was possible to maintain tension on the 
bridge unchanged.



  Adjustment trimmer potentiometers
R2 and R5 achieve compliance in three
Signs reading digital display
meter values ​​of the temperature of the thermistor TK1 and 
TR2-controlled accurate thermometer. In its absence can be used 
for medical temperature control in predelazh its scale and 
stable temperature of melting ice - 0 degrees.



                      (C) radio, N3, 1999.

                          B. Ratnovsky

                          Samara


  Click to view <V> scheme, in view ss +4 - screen recording;
edit, break - to exit the viewer.



  PS: Now about copyright'ov,
arranged in my articles.

  So, I'm not in any way do not pretend
the title of the author of these developments, and
this case only to emphasize that
I dug up this stuff and gave dany
it to you. I think that the authors of these materials, and our 
dear readers will understand my actions and will not be more to 
claim. 


                   Sincerely Mr.Linker


                      28.04.99 IS-EDITOR