LUMENIS VersaPulse PowerSuite - Page 68

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Refer to 8-12 in Section 8. Coolant resistivity and temperature are monitored by sensors that report an analog
voltage to the microprocessor ADC circuit. The software checks the coolant resistivity and temperature at
regular intervals in the following manner:
• The coolant is nonconductive (deionized) to minimize galvanic corrosion and high voltage
arcing in the cooling loop. It is monitored by a probe and the signal amplified (WATERRE-
SIST) in order to be read by the CPU. It will disable the system if the resistivity exceeds soft-
ware limits. A message "CHECK FILTER" will appear on the LCD display. Note that the
conductivity is effected by the action of the D/I filter. If the resistivity is low, running the
system in its standby condition will allow water circulation through the D/I filter, eventu-
ally raising the resistivity to an acceptable level. Resistivity will tend to be lower when the
unit is first turned on, then increase as the D/I filter removes charged particles. The D/I fil-
ter is a consumable item, and should be changed annually, or sooner if coolant resistivity
problems occur.
A 100Hz output signal (RESIST_100HZ_CLK/FSCLK) from the Digital Input/Output
EPLD U39 leaves the Controller PCB at J9-5 and is routed to the resistivity sensor
where the signal is applied across a one cm gap in the coolant. The other side of the
one cm gap is sensed at J9-6 (CONDIN), and input to the transimpedance amplifier
U29-2. the output of the U29-1 consists of positive and negative pulses. The individ-
ual pulses are selected for input to the positive and negative inputs of U27 by the
action of U33 as driven by the polarity of the RESIST_100HZ_CLK signal. The output
of U27-6 (TP34) as measured in volts, represents resistivity, where
Resistivity = (1/Voltage @ TP34) 10
6
(e.g. 1/2 Volts = .5 X 10
6
= 500k:)
• The software checks the coolant temperature (WATER_TEMP) at regular intervals, provid-
ing overtemperature disable ("OVERHEATING" displayed on the LCD color display) when
the coolant temperature reaches a set point. The disable clears when coolant temperature
falls to a reset point. Note that for every 1• C rise in water temperture is equivalent to a .1V
rise in output. Therefore the following table would apply:
Set Point for the Ho:YAG & Ho/Nd:YAG = 60• C, Reset Point = 55• C.
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Vol ts Ce lsi us
0.0 V 0• C
0.1 V 1• C
1.0 V 10• C
2.0 V 20• C
5.0 V 50• C