"Yes sir, it's designed to do that" - Well, not in so many words, but that's what it boils down to.
Regulars may remember my mini-rant about my Fluke 233 meter. That's the one whose head unit can be removed to remotely monitor the measured quantity. One of the features they don't mention though, is that even if you don't use it at all, the batteries will run flat within 4 months. Both base and display units (which have a total of 5 AA cells) draw around 1mA even when both units are OFF.
This week, finally spurred on by reports both on here and on Element-14's site (
http://www.element-14.com/community/thread/7523?tstart=0 ) I decided I should approach Fluke and ask if this was intended to be normal, and if anything could be done about it. Here is the response that got posted to the Element-14 forum (I have had no personal email reply yet). It is a public forum, so I feel able to re-post here. I have added paragraphs and spacing to make it readable, as the original poster seems not to know how to do so;
Hello Viewers, The 233 is unique in its design and implementation with its wireless display utilizing both iR and RF communication between the meter base and the remote display. While docked the meter utilizes iR communication and when the display and base are separated RF communication is used.
When new the meter is shipped with paper tabs inserted into the battery compartment for both the base and the display to keep the batteries disconnected from the meters power supplies. This is to insure that the batteries have a full charge and the customer gets the longest battery life possible. The reason for a short battery shelf life is that when the meter is turned off and the display is mated, the iR communication is still active. This was done by design to give the user the most flexibility when using their 233 meter.
The design allows the user to power on and to wake up the meter while the display and body are disconnected. It simplifies the meters operation. This use model was important to customers during our initial research for the 233. The alternative would have been to have two separate power buttons, one for the base and one for the display. Our research indicated that this was a less attractive solution to our implementation of one power up option for both parts.
The trade off is the unit consumes more power but gives the users more flexibility. If the meter were to go into battery save mode and the iR communication were not active, the display and meter body would need to be re-connected before the display could power up. This option and two separate power up processes were not attractive in our research.
To optimize the battery life, for intermittent use or extended periods of storage, it is recommended that the paper tabs be re-inserted into the battery compartments or the batteries be removed completely.
Jim Newell Sales & Application Engineer Fluke Corporation
(My bold emphasis)
I'm stunned! Not only do they see this battery life as acceptable and what their customers asked for, they actually want me to take the batteries out or insert fiddly paper tabs when I think I may not be using the unit (unfortunately I don't have foresight so am unable to comply with this).
I am going to make some recommendations:
1) As a short term fix, that the base unit only transmits maybe a couple of times a second, thus hugely reducing the average current load needed to constantly transmit. Additionally, reduce the IR LED output power by increasing the value of the series current limiting resistor.
2) That their next design revision uses either a mechanical or magnetic switch to detect when the display unit is undocked. It could even have electrical contacts in the docking rails that are shorted out and are detected as open circuit when undocked.
3) That the micro in the display be programmed to react to in interrupt generated by the IR LED rather than being permanently active (as it appears to be).
4) If they can't get it sorted then they should supply rechargeable batteries and a charger, or integrate one.
Maybe Fluke should employ fewer sales and marketing people and 1 or 2 more design engineers? Jeez...
Mike