Philips epiq 7, User Manual

Page: 236 / 318

Symbol Definition
S1 Open earth lift ground switch
S2 Line polarity switch
S3 Microammeter switch
L Line mains supply
N Neutral mains supply
E Earth ground
Current I, driven by line supply e, flows through all stray capacitances between the primary
wiring and the ultrasound system’s metal chassis. Ordinarily, current then flows from the metal
chassis through S3 and back to e through a third-wire ground. When S3 is thrown in the other
position, current I is forced:
• From the chassis through the metal parts of the transducer
• Through impedance Z, produced by the insulating layer that covers the metal parts of the
transducer and the saline solution
• Through the test electrode
Saline generally presents an impedance of about 500 Ω, so Z will vary between 850 kΩ and
500 Ω, depending on whether or not there is a conductive pathway caused by a hole in the
transducer’s insulating layer.
CAUTION
Do not make a DC measurement of impedance. This could set up a voltaic cell, with the metal
of the transducer and a test electrode in the salt bath forming the two electrodes and an
electrolyte. Such a voltaic cell produces inaccurate resistance measurements.
You need the following equipment to perform the electrical safety check procedure:
• Dempsey 432HD or 232D safety analyzer or equivalent
• Philips 21110A Disinfection Basin or equivalent
• Saline solution, 9 grams (0.3 oz) of salt to 1 liter (1 qt) of tap water, or one of the tested
disinfectants listed in the “Transducer Care” section.
Transesophageal Transducers TEE Leakage Current Test
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