Re: Personal Air Sample Problems

[lindsay@tremethick.fam.aust.com]

> The low battery charge may be due to the infamous 
> NiCad "memory" problem.  If NiCads aren't fully 
> discharged and recharged, i.e., if you recharge them 
> before they are absolutely dead, they will form 
> a "memory" at that level of discharge, and will not 
> provide the full battery capacity after that.  LiH and 
> other battery types do not do this, but I'm not sure 
> they are supplied in the typical personal air sample 
> pump.
> 
> The low flow problem could be a subset of the memory 
> problem.
> 
> The "fix" is to fully discharge the pump battery after 
> each use.  (Yes, it is a major hassle.)

Can't agree more. NiCads need to be exercised on a 
reasonable regular time frame which means drawing the 
desired current from them till they are flat. Generally the 
easiest way is to set up a bank of light globes that will draw a 
similar but slightly lower current as the pump. Connect it up 
and leave it to discharge, the lower current draw sort of 
"tricks" the Nicads into continually supplying current until 
completely flat. Once you have got to this stage and 
everything has cooled back to room temp recharge the 
batteries fully (possibly 18hrs on a trickle charger). Hopefully 
you will get a few more months out of the unit. When it finnally 
does die replace the battery with the nickle metal hydride type 
for less problems.

Yes the low flow may be related or dare I say it,..........
Is the person being monitored trying to vacuum up dust with 
the unit or simply blocking the end off???? I have struck this 
when I did some vocational work during my uni days. It is 
amazing what people will do with safety monitoring equipment.

Good Luck

 
Lindsay Tremethick
lindsay@tremethick.fam.aust.com
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html