Measurement & Laboratory Technology
The electronics of a measuring device for hazardous areas, split across ten circuit boards
Hardware development for the next generation of a process measuring device that operates in hazardous areas. Seven types of protection in one device, an extensive specification, and a development process that builds in review by the client and the certification body from the start.
The task
A measuring device for hazardous areas places demands on its electronics that go far beyond the measuring function. Every power supply, every external interface and every sensor connection must be designed so that it cannot become an ignition source even under fault conditions, and the design must be backed by evidence that satisfies the certification body.
The client wanted to renew the electronics of its measuring device: more compact, cheaper to manufacture, with more interfaces and a display. The device had to combine seven types of protection, including a flameproof enclosure for the main electronics, increased safety for the external connections and intrinsic safety for the sensor and signal paths. On top of that came a specification that defined everything from temperature ranges to component availability. Our task was the hardware, from concept to bring-up; mechanical design, firmware and regulatory approval remained with the client.
The solution
We split the electronics across ten circuit boards: a main board with a processor module, a backplane in increased safety for the external connections, plug-in interface cards, plus sensor electronics and an operator panel board. Each card identifies its slot and type through an address chip, so the firmware recognises the configuration without anyone having to set jumpers. Everything that has to be intrinsically safe sits on separate cards with their own design; what stays inside the flameproof enclosure does not need an intrinsically safe design, but is still subject to the requirements for the device as a whole.
The development process was geared to regulatory approval. The schematic and layout of every board went to the client and the certification body for review, and the boards were developed in a fixed order so that the intrinsically safe parts could be reviewed first. Before first power-up, every board had a bring-up plan approved by the client.
We delivered the design and manufacturing documents for all boards, the design of the intrinsically safe circuit sections as input to the client's regulatory approval documents, the bring-up reports and the system test plan. We also organised qualification with the test labs.