Harald Vefling

Trial Implementation of a Wireless Human Machine Interface to Field Devices

In order to configure field instruments today, it is necessary for the operator to approach each device and program it using the human-machine interface (HMI) placed on the instrument. This paper describes a demonstrator concept of how to use wireless communication and a portable device to achieve this at a distance, and simultaneously with several instruments. The major problem that has to be overcome in order to use wireless communication is the severely limited power available. The instrument in question is running on a 4-20mA current loop, and the power for the wireless communication comes from the available internal current in the instrument, in this case limited to 400muA at 3.0V. Since the available power is constrained, the radio is duty cycled so that it mostly sleeps, and transmits only when there is power available.