Battery life, portable instruments

Development of a Diffusion Head Sensor Cell. The use of air sampling pumps in portable electrochemical gas detection apparatus introduces potential problems into the instrument. First, the sensor cell response is dependent on gas flow rate. The sample flow rate, therefore, must be accurately controlled to obtain reproducible results, or the sample flow rate must be set high enough to insure a flow independent response. Secondly, failure of the pump itself could prevent a sample from reaching the sensor cell. Thirdly, the pumps are usually one of the largest users of current in a portable instrument and thereby limit usable battery life. 

For portable sampling systems, the response time should be quite short because the sample is being taken from the surrounding environment, or from a nearby location such as inside a confined space. Portable instruments with internal pumps can provide continuous readings of vapor concentrations. Their use is limited only by the life of the battery pack. 

In designing portable instruments, one of the considerations that must be taken into account is that they should be very user-friendly, as they need to be used in the field and should work quickly. Ease of use is important as nonscientists need to be able to use these instruments in certain situations, and the speed of obtaining the result is important from a battery life perspective. Portable devices should ideally give no false positive results but, in the real world, this means they should be as accurate as possible as the resultant data are often used there and then to make important decisions. Einally, they should be robust and easy to maintain and they should have enough memory to store the pertinent data obtained, at least until the user returns to a base station. 

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