??? 07/22/04 10:28 Read: times |
#74677 - Try this circuit! Responding to: ???'s previous message |
I already tried the voltage divider, but the voltage differs so little, that the adc can't measure it.
Hallo Andrej, if you use the KTY11-5 in a voltage divider design, you need a buffer with gain, of course! A suited circuit is shown here: ![]() Which resistors you should use, mainly depends on temperature range of interest. The above formula helps to get the circuit work. As a hint: Upper resistor of R1 should be about 5kOhm. This limits the current through KTY11-5 to less than 1mA, according to a recommendation of datasheet. Trimmer of about 220 Ohm helps to adjust manufacturing tolerances of KTY11-5 and resistors to some degree, and also helps to eliminate influence of offset input voltage of operational amplifier. R3 can also be in the range of about 5kOhm, R2 about 20kOhm and R4 about 33kOhm. This, only as a starting point for experiments... Take care, that the reference voltage for the voltage divider, Uaref, is identical with reference voltage of ADC of microcontroller! Then, changes of Uaref will not cause additional errors, but cancel, fortunately, as the above formula shows (Uout is linear with Uaref). R1 plays an important role: It's mathematically connected in parallel to KTY11-5 and helps to linearize KTY11-5 to some degree! If an unlinear resistance is paralleled by a linear one, resulting circuit is less unlinear than unlinear resistance alone. This works so good, that for applications not demanding highest precision the parallel circuit can be thought to be linear. If you need high precision, on the other hand, you must take the unlinearity into consideration and fabricate corrected temperature reading by the help of a suited look up table. Values between stored data points of look up table can then be calculated by piece-wise linear interpolation. Kai |
Topic | Author | Date |
Temperature senzor | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
RE: Unhelpful | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 | |
Try this circuit! | 01/01/70 00:00 | |
RE: Try this circuit! | 01/01/70 00:00 | |
RE: Try this circuit! | 01/01/70 00:00 | |
RE: Try this circuit!![]() | 01/01/70 00:00 | |
RE: Temperature senzor | 01/01/70 00:00 |