Gymna Pulson 330, Service Manual

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12. US power and output stage.
12.1 Measuring and displaying US power
When the INT_UP key is pressed, a certain output voltage (1 or 3 MHz)
is obtained, and the crystal starts vibrating on resonance frequency.
However, not all electrical power is transformed into acoustical
vibrations. Since the crystal has a certain resistance during
treatment, heat will be produced as well.
Consequently, different crystals may have different efficiency
factors, which can be measured in a test lab. After measurement, each
crystal gets a resistance, which represents this efficiency factor.
The microprocessor is able to read this resistance and to process this
value, in order to display the right output power.
This means that with a low efficiency head, the pulson will display
less output power than with a high efficiency head. This resistance is
therefore soldered into the plug of the treatment head.
Pi is the
input power,
calculated by measuring
US_VOLTAGE and US_CURRENT.
Pu is the output power in an ideal medium ( 0% reflections ).
Pu = Pi *
η
head *
η
output stage
The R_POT value represents the efficiency of the head (
η
head), and is
constantly monitored by the
µ
processor. It also makes it possible to
see whether the head is connected or not.
The efficiency of the output stage (
η
output stage ) is determined
during calibration and its value is saved in the eeprom.
Knowing these values enables the
µ
p to calculate and display the
output power.
Output power is determined in following way:
1. User presses INT_UP key
2. A certain output is obtained.
3. Current and Voltage information are sent to the
µ
p.
4. The
µ
p calculates the output power, thereby taking the efficiency
values into consideration.
5. The user can see the output power displayed and can change it by
pressing the INT_UP/DOWN keys.
In other words, some measurements are performed, the output power is
displayed and the feedback is performed by the user himself ( by
pressing the intensity keys).
Notice that US_VOLTAGE and US_CURRENT are both peak values.
Measuring of these values is done just before the end of the US-pulse,
or in case of the continuous ultrasound mode 32 times per second.
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