Analog Signal Conditioning for Accurate Measurements

Q: Should I put some sort of circuit between my and an -to-digital converter?

A: Yes. You probably need some . The explanation in this paper goes on for a bit, but stay with it and you'll understand what you need and why you need it.

Before you make any connections, get the electrical specifications for the analog-to-digital converter () and for the sensor or in your system. Let's assume the data-acquisition module uses a Maxim Integrated Products MAX197 12-bit ADC. This can accept eight differential () inputs or 16 single-ended (1-wire) inputs. Maxim's specifications show an input impedance of 21 kohms for single-ended inputs and 16 kohms for differential inputs.

Now let's assume your system uses an AD590 in a simple circuit (Figure 1) to produce a 1-mV/K output. The sensor serves as a source that passes 1 µA per (K), or per degree (°C). The Kelvin scale uses the same increments as the Celsius scale, but it starts at absolute zero: 0K or -273°C. At 0°C, the Kelvin scale reads 273K and at 25°C it reads 298K. The Kelvin symbol does not include a degree mark.

Advertisement