Calculating Current Draw - Teledyne 4250 Installation And Operation Manual

4250 Flow Meter
Section 1 Introduction
1.9.1 Calculating Current
Draw
1-14
Batteries lose capacity as they age. Capacity also drops off as
temperature falls. Low temperatures make less capacity
available due to the slowing of the chemical reactions, while high
temperatures accelerate the deterioration of battery plate sepa-
rators, particularly if they are aged. Nickel-cadmium batteries
show fairly rapid rates of self-discharge. A battery that is fully
charged and then placed in storage will lose some capacity each
day. In a week, this could easily be 5% or more.
When using lead-acid batteries, you must be careful to avoid
complete discharge, as this may cause cell reversal, which will
ruin the battery. Also, complete discharge in low temperature
ambients may cause the battery to freeze, which can deform the
plates or even crack the case. Always operate these batteries
with a reserve factor.
Calculating current draw for a 4250 Flow Meter is somewhat
more difficult than calculating the battery capacity. You cannot
simply measure the idle current of the unit unless the printer
and report generator are turned off in the program. These func-
tions require power periodically, but not all the time. If the
figures given in the previous table are not satisfactory for your
application, you can use the following procedure (shown in
Figure 1-6) to measure the actual current draw.
Note
Do not attempt this procedure unless you have the proper
equipment available and know how to make electrical mea-
surements.
To measure current for a varying load requires a more-sophisti-
cated type of multimeter, one that is capable of averaging high
and low readings over a period of time. The Fluke® 87 Multi-
meter is one example of this type of meter. You should set the
meter on MIN/MAX and let it run with your program for several
hours or more. Other manufacturers' meters are also acceptable,
but only if they are capable of averaging current draw. For a more
representative test, the area-velocity sensor should be attached
and submerged in water. You should run the test for at least
eight hours, longer if necessary, or until the flow meter has exer-
cised the entire program. The longer you run the test, the more
accurate the average will be.