Hand Hygiene

testing

Magnet Info:

• Size and shape play a large role in determining the strength of a magnet.
• The grade of a magnet directly refers to its Maximum Energy Product [MGOe].  Generally, a higher grade represents a stronger magnet (i.e. for a neodymium magnet, grade 40 = N40 = 40 MGOe)
• Alnico magnets are manufactured by either sintering or casting.  Sintering = higher mechanical strength, Casting = higher energy product
• Pull force tests are not standardized

• General strength according to material:
  

  Material	Strength	Pros	Cons
  Ceramic	Low to Medium (grades 1 – 8 )	Low cost High coercive force High resistance to     corrosion	Low energy product Low mechanical strength (brittle)
  Alnico	Medium	High resistance to corrosion High mechanical strength High temperature stability	High cost Low coercive force Low energy product
  Rare Earth (neodymium-iron-boron, samarium-cobalt)	High to Highest (grades up to 52)	Very high energy product High coercive force	High cost Low mechanical strength (brittle)
  Flexible	Very low	Low cost High resistance to corrosion Moderate coercive force	Low energy product Low to medium temperature stability

  References and suppliers:

  • www.mcmaster.com
  • www.supermagnetman.com
  • www.rare-earth-magnets.com
  • www.allmagnetics.com
  • www.kjmagnetics.com

The same test was run with the Purell (9 configurations, 3 angles, 3 locations) to see if the handwash credit goes to the right person at .5 and 1.5 meters and .5 and 2.5 meters.

Here are the results:

Data for .5 and 1.5 meters with the right hip was not available because the data couldn’t be downloaded. We still see a huge variation. Maybe we can improve our testing method?

Geb and I tested the Purell data to if handwashing credit goes to the right person. We stood with three pagers on our left/right hips and chest and recorded data from .5 and 1 meters away (the value stated on the graphs is wrong). We conducted this test with 9 different configurations, at three angles.

From the data, we see that the best location for the pager is the right hip. We also see that the worst location for the pager is the chest. There is a lot of variability in the data. maybe increasing the distance will help.

I have written a new trigger program which records the time of each pump to flash. The time it records is local mote time, so remember to note the time the trigger was turned on. The program makes the blue LED turn on whenever the pump is pushed down. If the mote fails to write to flash, the red LED will flash.

It is on the Ubuntu computer upstairs in ~/Desktop/newtrigger . It contains subdirectories for reading and clearing the flash. Refer to the readme in ReadFlash for information on how to read the flash.

The three modified triggers are currently programmed with this program.

Bed Motes

-need a better location for bed motes (more accessible)

-need to be attached to surface differently – magnets didn’t work; sticky tape didn’t allow it to be adjusted and was hard to get off after the experiment

-motes need to be attached in box differently – sticky tape wasn’t sticky enough; USB cables could come off easily

-next time, add batteries?

Pyramids

-need longer cables to plug them in

-put a sticker in a more visible location to identify it as part of the experiment

-put a “This Side Down” sticker on the bottom to avoid people flipping them over

-try to cover the switch so nobody can turn it off

Pagers

-check all the USB/charge lights with the cables we use

-figure out the flash problems

-lighter design? towards the end, nurses still complained about the weight

Pucks

-more sturdy – pucks take a lot of beating depending on the day and the person using it, so they need to be able to stand up to that; the screws also started to come loose toward the end of the experiment

-keep the blue light visible

-simpler hardware – taking them apart to replace a battery or adjust the sensitivity took a lot of time

-put out new designs in the hospital earlier to see the problems they face – different people pump differently and it would be really hard to mimic that in the lab

-come up with something for free-standing bottles

-need something that wouldn’t be as complicated to replace and/or to change out bottles

We’ve been working on a couple new ideas for the triggers.  The first is a touch activated switch.  I put some aluminum tape on the top of the soap dispenser and connected it to a capacitive sensing circuit.  It works most of the time, but occasionally misses.  We might be able to balance the sensitivity and reliability of this, but we’ll need some way to make the top of the bottle conductive.

A single lead connects the evaluation board for the PCF8883 (the UM10370 board from NXP Semiconductor) capacitive proximity switch to the aluminum tape on the lever.  A light touch triggers the indicator light.

The second idea is to use a magnet to trip a reed sensor located inside the bottle.  This seems like a very convenient technique, but we’re not confident that we can get the right combination of magnet and reed sensor so that we can make a repeatable process that doesn’t require lots of tweaking.  The magnet goes inside the plunger mechanism and the reed goes on the outside of the foaming chamber.  This demo seemed to work pretty reliably, but required a movement of several mm before actuation.  Some minimum distance is required because there appears to be some hysteresis in the mechanism.

Gregg holds the demo he assembled.  The rectangular magnet sits in the gap between the clear plastic and the white top of the lever.  In the working demo tape holds the reed switch connected to the two leads.  When the magnet is close to the reed switch, it closes, which could trigger the mote.

It turns out the transmitters work fine with two AA batteries rather than three. This means it would be possible to put an ipod battery in the next version. An ipod battery has 3.7 v and 850 mAh, meaning it has 3.145 watt hours of energy. Two AA batteries have a total of 3.2 v and 1500 mAh, meaning they have 4.8 watt hours of energy.

There are also other lithium-ion batteries out there worth looking into. It would be nice if the next version of the door minder had at least as much battery life as the current one.

I’m thinking that the main problem with the puck design is the reliance on measuring force at the bottom of the bottle, which can be affected by the wire basket, which can absorb some of the downward force.  This requires the puck to be adjustable, which turns into a practical problem.  I’m thinking that conductive ink on the surface of the bottle lid connected to a capacitive sensor may create a more reliable signal.

We could use a chip to handle most of the measurements.  The PCF8883 is a capacitive proximity switch with auto-calibration, large voltage operating range and very low power consumption.  I’m ordering an evaluation board for this so we can check it out.

Ted points out that we could add bluetooth to the motes so we can use this handy keyboard.