Patent ID: 8777432

Claim:
A Human Machine Interface (HMI) device for connection to a programmable logic controller, comprising: a field bus interface connected to the programmable logic controller; an optical display field; a first light source arranged behind the optical display field of the HMI device and configured to generate a color to be generated as one of (i) an elementary color or (ii) a secondary color from elementary colors comprising red, green and blue; an activation module connected to the first light source of the HMI device and configured to activate the first light source in accordance with the color to be generated; a second light source arranged behind the optical display field of the HMI device and configured to generate the color to be generated, the second light source being connected to the activation module and the activation module of the HMI device being further configured to activate the second light source in accordance with the color to be generated; and a monitor configured to identify one of (i) an error and (ii) a fault on one of the first and second light sources and thereupon to shut down a faulty light source of the first and second light sources.