Alnor 9870, Owner'S Manual, Page: 10 / 21

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past 3 seconds. The way the meter averages
velocity is by saving the velocity measured each
second into separate locations in memory. Every
second, a new reading is taken and the oldest
reading is thrown out. Depending on the position of
the sensor response switch, either the last 3
readings or all 12 readings will be averaged for
display.
Batteries
The Model 9870 is powered by four AA-size
batteries. TSI ships the instrument with alkaline
batteries, but nickel-cadmium rechargeable
batteries may be used. Keep in mind that battery
life is a function of the velocity being measured: the
higher the velocity, the shorter the life. Table 2
shows typical battery life for both alkaline and
nickel-cadmium batteries at three velocities.
Table 2: Typical battery life* at three velocities
Air Velocity
alkaline
life
nickel-
cadmium life
(fpm) (m/s) (hrs) (hrs)
100 0.5 10 2-1/2
1000 5.0 6 1-3/4
2000 10.0 5 1-1/2
* At 20°C