Older machines and manufacturing plants can usually be retrofitted with a wide range of sensors: These range from sensors for measuring lube oil levels, or simple counters to vibration sensors for early identification of anomalies. This is called retrofitting.
Typically, such retrofitting is carried out with the aim to establish an Industrial Internet of Things (IIoT) so that machines can exchange data with each other or data can be combined and evaluated for quality control purposes. Communication standards such as OPC UA or MQTT are used.