FDT-25 Handheld Ultrasonic Flowmeter
7
2. Starting Measurement
§2.1 Built-in Battery
The instrument can operate either from the built-in NiMH rechargeable battery, which will last
over 10 hours of continuous operation when fully recharged, or from an external AC/power
supply
from the battery charger.
The battery charging circuits employ a scheme of constant-current and constant-voltage. It has a
characteristic of fast charging at the beginning and very slow charging when the battery approaches
to full recharge. Generally, when the green LED starts coming on, the battery would be nearly
95% recharged and when the red LED is off, the battery would be 98% recharged.
Since the charging current becomes tapered when the battery recharge is nearly completed, i.e.
the charging current becomes smaller and smaller, therefore, there should be no over-recharging
problem. That means the charging progress can last very long. The charger can be connected to
the handset all the time when an around-the-clock measurement is required.
When fully recharged, the terminal voltage reaches around 4.25V. The terminal voltage is displayed
on window M07. When the battery is nearly consumed, the battery voltage drops to below 3V.
The user can obtain an approximate battery working time from the battery voltage.
A software battery working time estimator is integrated in this instrument based on the terminal
voltage. Please note that the estimator may have relatively bigger errors in the estimated working
time, especially when the voltage is in the range of around 3.70 to -3.90 volt.
§2.2 Power On
Press the ON key to switch on the instrument and press the OFF to turn off the power.
Once the flow meter is switched on, it will run a self diagnostic program, checking first the hardware
and then the software integrity. If there is any abnormality, corresponding error messages will
display.
Generally, there should be no display of error messages, and the flow meter will go to the most
commonly used Menu Window Number 01 (short for M01) to display the Velocity, Flow Rate,
Positive Totalizer, Signal Strength and Signal Quality, based on the pipe parameters configured
last time by the user or by the initial program.
The flow measurement program always operates in the background of the user interface. This
means the flow measurement will keep on running regardless of any user menu window browsing
or viewing. Only when the user enters new pipe parameters will the flow meter change measurement
to the new parameter changes.
