In order to choose sensors correctly, it is necessary to understand for what measurements they are applied and how reliable is the result of measurement. Mostly, 4 temperature sensors are used: thermistors, digital semiconductor, thermocouples & RTDs.
Specifications of platinum and copper RTDs, thermistors and thermocouples: tolerance classes, operating ranges, acceptable accuracy, etc.
Calibration is testing of measuring instruments with the purpose to confirm their accuracy. Each instrument should be calibrated before it is shipped out. Usually one year of calibration period is specified in the certificate.
When using resistance temperature detectors (RTDs) for temperature measurement, the additional error can be introduced by connection wires, as wires have their own resistance which depends on the ambient temperature.
For measuring of air relative humidity several types of hygrometers are widely available. They are Capacitive and Resistive RH Transmitters, Psychrometers and Aspiration Psychrometers.
Psychrometric method of air humidity calculation is based on the fact that the temperature difference between wet and dry thermometers depends on the air humidity.
On-off control with one or two setpoints, three-position control per one or two units, multi-zone control.