# Pistons and microprocessors

1. Jun 9, 2014

### Nerdydude101

So in an insulin pump there is a cartridge that holds 200 mL of insulin, this is broken into 200 "units" of insulin (i would use metric but i can't seem to find the proper metric prefix for 1x10^-5). The piston is controlled by a microprocessor and gives these very small "units" of insulin, the smallest it can give is .05 of one of the "units" my question is how hard is it to get a piston to move that exactly?

2. Jun 9, 2014

### thankz

not that hard if you use a stepper motor with a screw drive setup.

3. Jun 9, 2014

### Staff: Mentor

Or even a microstepper motor with the screw drive...

4. Jun 11, 2014

### Baluncore

There is no SI prefix for 1x10^–5. It is 10x10^–6 = 10 u.
If a 200 mL cartridge holds 200 “units” then each unit is 1 mL.

0.05 mL is an interesting volume. It is the approximate volume of one drop of water.
If you use a common eye dropper, 20 drops = 1 mL.

Intravenous drips are regulated by counting drops.
Different profile drippers have different drop volumes. Standards are 10, 15, 20 or 60 drops per mL.

http://en.wikipedia.org/wiki/Drop_(unit)