Author Mazi Hosseini describes a simple, low-cost, voltage-controlled current source using two op amps that provides a good range of current and maximum load.

This Design Idea mates a precision current source IC with precision difference amp chips to create a programmable current source or sink. The resistor-programmable current source/sink in Figure 1 ...

A current source provides electrical energy with a constant current. The implication is that if the resistance of the load changes the current source will vary the voltage to compensate.

You can achieve accurate resistance-temperature-detector sensor measurements without having to resort to using a precision current source.