Every data logger with analogue or digital inputs will have at least one sensor connected to measure a specific parameter. Some sensors are built into the data logger such as single channel temperature and humidity loggers, while others will be connected externally.
Some of the most common parameters are Voltage, Current, Resistance, Frequency, Temperature, Humidity, Pressure, pH, Wind Speed and Wind Direction, Strain Gauges, Rainfall, Moisture and Leaf wetness, Vibration, Acceleration, RF, Light, Sound, Time, Logic on/off, Rotary Encoders, Serial data, SDI-12 & MODBUS data. And the list goes on!
General purpose data loggers can usually measure industry standard output signals like 4-20mA current or 0 to 10 volts DC and many of the parameters listed above will been measured with sensors that output one of these signals or similar.