Monday, July 9, 2012
TMP36 Temperature Data Logger
In this blog I use a simple 3-pin Centigrade temperature sensor, TMP36 (in a TO92 package) as input to the data logger. One pin connects to ground, one to +5V, and the third to the analog input of the DAQ.
I simply want to demonstrate the system's ability to record a series of temperature readings and to display them in a graph. To make the graph interesting, I will hit the sensor with freeze spray, followed by a heat gun.
LabView is a graphical automation program. The programmer works from 2 main screens: the 'front panel' on which virtual instruments, displays and buttons reside, and the 'block diagram' in which graphical coding takes place. The big grey rectangle that encompasses several icons in the white-space above is in fact a software loop. Loops are used to repeat functions (in this case, measurements) indefinitely. The first blue box to the left represents the analog voltage measured by the myDAQ. At room temperature it reads 750mV. According to the temp sensor's data sheet, the TMP36 has an offset voltage of 500mV; with scaling of 10mV/degC. The easy conversion of voltage to temperature is .750V - .500V * 100 = degrees C, or 25.0C (standard room temperature). I perform this mathematics using triangular icons for subtraction (with a constant of .5) and multiplication (with a constant of 100). The second blue box is a 'write to measurement file' icon, which actually does create a TDMS file on my laptop computer. All of this takes place inside of the loop (at a thousand samples per second). The third blue box, situated outside of the loop, is the 'read from measurement file' icon, which when the stop button is depressed, it reads back the stored data. This is wired to a graph icon, which displays the data graphically. It may sound silly; but this kind of graphical programming is extremely powerful. I composed this in an hour; were I to attempt the same using any other common programming language; it would have taken at least a week.
TMP36 Sensor from Digi-Key [Link]
Picture of Test Setup [Link]
Program Up Close [Link]
My other interests [Link]