Doubts about temperature measurement simulator AD590

zhengzhoutie

Doubts about temperature measurement simulator AD590 [Copy Link]

Recently, when I was measuring high temperature, I used to choose the DS18B20 of the digital converter. Because of its low accuracy, I wanted to use the AD590
But the problem arises-----
R2 in the circuit converts the current output by the ad590 into voltage, but I use a 1K resistor to adjust it in zero degree water, and the output current seems to be non-zero. Why?

[ This post was finally edited by zhengzhoutie at 14:16 on July 7, 2009 ]

zhengzhoutie

The picture is here

zhengzhoutie

Not on the picture, alas: L

xiaoxif

You ask: The output current does not seem to be zero when adjusted in 0 ℃ water. Why?

Why did you ask this question? It can be seen from this question that you have not read (at least not carefully read) the AD950 materials. Note the following statement:

For supply voltages between+4 V and+30 V the device acts as a high efficiency, constant current regulator passing 1 μ A/K. Laser trimming of the chip's thin film resistors is used to calibrate the device to 298.2 μ A output at 298.2K (+25 ° C)
This passage means:
The power supply voltage is in the range of+4 V to+30 V, which can be regarded as a high impedance constant current source with a conversion coefficient (i.e. conversion sensitivity) of 1 μ A/K. (Note K).
Product factory fine adjustment calibration It is carried out at 25 ℃ (=298.2 ℃ k), and the output should be 273.15 μ A at zero ℃. Of course, more than 270 millivolts will appear. If you try to use the curve of y=ax+b, it will be clear at a glance.
If expressed in degrees Celsius, the relationship is: I=a * T+273.15; A=1 mA/° C

Of course, these are "theoretical values", or design values. It must work within the recommended temperature measurement range. If you need to output 0 at 0 ° C, you need to do further circuit design or use software to solve it.
.

[ This post was last edited by xiaoxif at 23:12 on July 8, 2009 ]

zhengzhoutie

Thank you upstairs. I'm dizzy. Go down and think about it------------------------
However, the problem now is that the ad590 outputs 270uA at zero degrees, OK! Put it in 50 ° water, its current is only 284. The circuit is directly connected with a 10K resistance. What's more strange is that if you reduce the 10K resistance, the current will rise. Why??
Is there something wrong with the device??
The answers given by ls are very detailed. I am very benefited,