Sonics VC500 - Manual (Page 10)

10
TUNING
Tuning optimizes performance and insures maximum transfer of energy by matching the
frequency of the power supply to that of converter/probe assembly. The power supply
should be tuned 1) every time a new probe or accessory is used, 2) on occasions to
compensate for the frequency variation caused by cavitation erosion 3) following 10
minutes of continuous operation and 4) when the sample temperature is significantly
higher or lower than room temperature.
The piezoelectric crystal within the converter is part of the circuitry, which controls the
frequency at 20kHz. Any changes in t the crystal’s capacitance resulting from a variation
in temperature, will cause the equipment to operate in an out-of-tune condition. For
reliable performance, and equipment protection, it is important that the unit be tuned after
the probe temperature has had a chance to stabilize. When relocating the ultrasonic
processor from a very cold or very hot environment, allow 30 minutes for the unit
temperature to stabilize before operating. Continuous operation causes temperature
elevation in the sample. This increase in temperature is transmitted through the probe to
the crystal assembly. Always tune the power supply after the probe has reached operating
temperature. When working with low or high temperature samples, immerse the probe in
the sample for a few minutes, withdraw the probe from the sample, then tune the power
supply.
1. Ensure that the probe or microtip is not immersed in the sample and that it does
not come in contact with anything. If a cup horn is used, make sure that the water
has been drained out of it. If a flow through cell is used, make sure that the
sample has been drained out of it.
2. Set TIMER to HOLD.
3. SET output control to “10” (to “4” when using a microtip of extender).
4. Momentarily hold down On/OFF/TUNE switch to TUNE and rotate the tuning
control clockwise or counterclockwise until a minimum (not maximum) reading
(usually less than 20) is obtained on the power monitor. If minimum reading
(sometimes referred to as null) cannot be obtained, the probe, cup horn, tip,
microtip, or accessory is loose or out of resonance, or the power supply or
converter require servicing. A loose probe will usually generate a loud piercing
sound.
IMPORTANT
Tuning must be performed in air with the probe out of the sample. While tuning,
do not allow the probe to contact anything.
CAUTION
When using a microtip, never allow the tip to vibrate in air for more than 10 seconds and do not set the
OUTPUT CONTROL above “5”. Ignoring these instructions will cause the microtip to fracture.