Dear Sir/Madam,
In our application we are using ADS1147 for measuring temperature from Pt100 sensor in a 4-wire measurement system. Our micro controller code is as per the pseudo-code example mentioned in page 65 of ADS1147 datasheet.
We have written the following values into configuration registers.
|
REGISTER |
VALUE |
|
|
MUX0 |
0x0A |
|
|
MUX1 |
0x20 |
|
|
SYSO |
0x3F |
|
|
IDAC0 |
0x06 |
IDAC Excitation Current Magnitude set to 1mA |
|
IDAC1 |
0x0F |
|
As mentioned in the above table we have configured the excitation current source as 1mA. Also by using RREG command the read back data from IDAC0 register is 0x96. This confirms our setting of 1mA. Our 4-wire RTD measurement is based on Four-Wire RTD Measurement, Low-Side reference mentioned in page 23 of application note sbaa275
Our RREF is 1.65k Ω and so the expected voltage across RREF must be 1.65V( 1.65k* 1 mA).
However, we are getting 2.46 V. So this indicates that the current is 1.5 mA( 2.46/1.65k) but not 1mA.
Why ?. Can you help us what is wrong ?
