I’m trying to connect three LM35 temperature sensors to my USB DrDAQ external ports (Ext1, Ext2 and Ext3). These sensors are powered from +5v out of DrDAQ. The readings of the sensors when connected to DrDAQ are wrong (24 C becomes 120 C), when I disconnect the output of the sensor from DrDAQ the readings are accurate (measured with DVM and compared to medical air temperature sensor).
The problem I think is with the internal 100k pull-up resistor, which is pulling the o/p of the LM35 high. What should I do to get an accurate measurement?