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MediPi Patient Device Build Instructions and Electromagnetic Conformance Testing
The MediPi Patient device is built using a Raspberry Pi with a touch screen display within a plastic enclosure. Although the Raspberry Pi, the screen and the power supply have individually been tested by the Raspberry Pi Foundation against the Electromagnetic Conformance specification, the unit as a whole has not been. Additionally, the standard for electromagnetic radiated emissions for electronic equipment which will be used for patients who may be using sensitive medical devices such as pacemakers is higher.
The biggest issues we had were controlling the Raspberry Pi unit's electromagnetic emmissions, which uncontrolled were too high. Controlling measures were iteratively taken and re-tested. This was a time consuming process as each iteration could take >1hr. Controlling measures included ferrite sleeves, shortening of excess cables and copper tape sheilding - see guide below. The final solution could probably be improved upon with more time.
Here are the 30MHz-1GHz improvements that were made:
Electromagnetic Conformance Testing was carried out at York EMC Services, taking 5 days.
Radiated RF Immunity, <1GHz
Radiated Emissions, <1GHz
Radiated Emissions, >1GHz
Semi Anechoic Chamber
Radiated Emissions, >1GHz
Radiated RF Immunity, <1GHz
Conducted Emmisions Test
EFT/B, Power lines
Conducted RF Immunity, Power Lines
ESD Test
Voltage dips and interruptions immunity setup
Mains Harmonic Emmisions And Voltage Fluctuations Test
Power Frequency Magnetic Immunity
EN60601-1-2:2007 + Corr.20
** Medical electrical equipment - Part 1: general requirements for safety. Section 1.2 Collateral Standard: Electromagnetic Compatibility – Requirements and tests.**
As tested by York EMC Services on 7th-21st April 2017
Stick the copper tape (cut into appropriately sized strips) on the inside of the boxed part of the enclosure. Place the strips side-by-side so that they touch and leave no gaps. Make sure the copper tape is pressed stuck on all sides and is firmly anchored in the corners. All the cut outs for the ports should be covered. Lastly add one small strip which covers the inside corner where there is a rebate for the LCD screen cable – this will make electrical contact with the copper tape and ground plane of the LCD screen.
Take the LCD Touchscreen and make sure that the standoff posts are firmly tightened (they often are loose from the package). Firmly lock the inter-board ribbon cable into the lower board (ribbon contacts facing upwards). Slip the ribbon cable ferrite over the cable.
Anchor the main LCD ribbon cable to the steel ground plane using black electrical tape. Make sure that it is not imparting any stress on these cables.
Stick a piece of copper tape over the black electrical tape so that it makes contact with the ground plane. The upper edge of this tape should be level with the top edge of the grey steel ground plane
Place the microSD card in the Raspberry Pi board and secure this to the LCD board stand-off posts using the provided screws.
Secure the remaining end of the inter-board ribbon cable into the Raspberry Pi
Pass each 10cm jumper wire through the axial ferrites twice and connect: GND on the LCD board to pin 6 on Raspberry Pi GPIO. 5V on the LCD board to pin 2 on Raspberry Pi GPIO
Anchor the ribbon cable ferrite at the bottom end using black electrical tape on both sides of the cable. This stops the ferrite from pulling the ribbon cable from the top of the raspberry Pi board in transit.
Carefully cut out the copper tape which is covering the power cable cut out in the enclosure back
Carefully place the enclosure back over the raspberry Pi board
Use black electrical tape to cover over the copper tape covered holes for aesthetic appearance
Wrap the power cable twice round the openable ferrite sleeve about 10 cm from the micro USB terminal end and snap lock closed