Touch Current Basics prepared for CTL PTP Workshop May 2010 Ronald - - PowerPoint PPT Presentation

Touch Current Basics

prepared for CTL PTP Workshop May 2010 Ronald Vaickauski Senior Staff Engineer Underwriters Laboratories Inc.

Human Response-Electric Shock

• Charles F. Dalziel,

University of California Berkeley

• W. E Hart,

Fluke Corp., IEC 66E Committee

Perception/Reaction Findings

IEC TR 60479-5:2007 Table 1

Let-Go Findings

IEC TR 60479-5:2007 Table 1 Values for current are in milli-amperes.

Ventricular Fibrillation

IEC TR 60479-5:2007 Table 1 Current is in milli-amperes.

Elementary Touch Current Network

IEC 60990:1999 Figure 3

Threshold of Perception

Figure 1 of IEC TS 60479-2:2007

Perception/Reaction Network

IEC 60990:1999 Figure 4

Let-Go Network

IEC 60990:1999 Figure 5

Calculated Impedance – Perception/Reaction Network

IEC 60990:1999 Table L.2

Calibration of Network

IEC 60990:1999 Table L.5

Frequency Range of Design and Calibration

• Frequency of Touch Current
• 50 and 60 Hertz Sinusoidal
• Electronic circuitry
• Non-Sinusoidal wave forms
• Fourier expansion
• Higher frequency components

References

• IEC 60990:1999, Methods of measurement of

touch current and protective conductor current

• IEC/TR 60479-5:2007, Touch voltage threshold

values for physiological effects

• IEC/TS 60479-1:2005, Effects of current on

human beings and livestock- Part 1: General aspects

• Measuring Touch Current – Resolving the

Controversy About Peak versus RMS; Hart, W.F.,Perkins, P.E., Skuggevig, W., 1997.

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Human Response-Electric Shock: Charles F. Dalziel, a professor of electrical California Berkley, did research on human book, “The Effect of Electric Shock on Ma for touch current are based on his work. Another major contributor was Walter E. H member of the IEC 66E committee and IEC

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cal engineering at the University of an response to electric shock and wrote a an.” Much of the requirements in place

• E. Hart, Fluke Corporation who was a

IEC TC 74 Working Group 5.

Perception/Reaction Findings: Perception/reaction current flowing through involuntary muscular contraction to the

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rough the body is just enough to cause he person through which it is flowing

Let-Go Findings: Let-Go current flowing through the body contraction of a muscle, such as inabilit from an a.c. electrode.

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body is just enough to cause involuntary ility to let go

Ventricular Fibrillation: Ventricular fibrillation current flowing thr cause ventricular fibrillation of the heart. human heart is in danger of failure to funct

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through the body is just enough to

• heart. Ventricular fibrillation is where the

ction.

Elementary Touch Current Network: The three component combination of the parallel combination of the 1500Ω resis the body impedance model. It represen electrical impedance of a person touchi resistor in parallel with the 0.22 µF capa impedance of the entry and exit skin con a conductive surface of equipment and

• contacts. The 500Ω resistor represents

skin, and serves as the current-sensing since all of the current that flows through through this resistor.

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f the 500 Ω resistor in series with the sistor and 0.22 µF capacitor comprises ents hand-to-hand or hand-to-feet ching a conductive part. The 1500 Ω apacitor represents the combined contacts (wet skin, not immersed) with and ground, or with two equipment ts the internal body resistance, less the ing resistor in the measuring circuit

• ugh the body impedance model flows

Threshold of Perception: The human bodies response to touch curren perception increases with frequency. The g 60479-2:2007.

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rrent varies with frequency. The threshold of e graph shown is figure 1 of IEC TS

Perception/Reaction Network: The touch current network for perception/reaction i the one most often referenced I product safety testin by a voltage-divider consisting of the resistor and current-sensing resistor. The frequency-weight designed to attenuate the voltage signal from the

• f the body current. The voltage transfer charac

Dalziel's data describing human responses for The frequency weighting network causes the in to the expected level of physiological response, measuring instrument is not a substitute for an instrument's response is not necessarily equal through the body impedance model. The readi adjusted by the frequency-weighting network fo

• frequency. Therefore, the reading can be compa

without knowing the frequency, and allowing a s limit for the physiological effect to be addressed. Actual RMS current measured through the 500 Weighted current indicated by the voltage after response to the touch current independent of fr evaluate current comprised of combinations of

• shapes. The weighted current is referenced to t

physiological effect.

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n is a frequency weighted network. This network is sting standards. The frequency-weighting is done and capacitor connected across the 500 Ω ghting network is essentially a low-pass filter the 500 Ω resistor according to the frequency racteristics of the network is designed from

• r perception or startle reaction.

instrument to have an indication that is related se, independent of frequency. A touch current an ammeter. The touch current measuring equal to the number of milli-amperes flowing eading of a touch current measuring instrument is for variations in human response due to pared to the limit value in the requirements a single numerical value for the touch current ed. 500 Ω resistor relates to electrical burns. ter the reaction is related to the body muscular f frequency. Weighted current is useful to

• f frequencies, including non-sinusoidal wave

to the 50/60-Hz current that produces a certain

Let-Go Network: The touch current network for “let-go” is a voltage transfer characteristics of the ne responses for the “let-go” response. The frequency weighting network cause indication that is related to the expected independent of frequency. The reading instrument is adjusted by the frequency human response due to frequency. The to the limit value in the requirements wi allowing a single numerical value for the

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s also a frequency weighted network. The network is designed to emulate human auses the instrument to have an ted level of physiological response, ng of a touch current measuring cy-weighting network for variations in herefore, the reading can be compared without knowing the frequency, and the touch current limit.

Calculated Impedance Perception/Reacti The performance of the Perception/Rea variable frequency sinusoidal current th terminals A and B. The input current ( I) voltage ( U2) are measured at various f voltmeter. Measured ratios of input voltage to inpu

• utput voltage to input current (transfer

compared with ideal values calculated f

• specific. In building the instrument, care

the circuitry so that inter-component capa characteristics of the voltage measuring the voltage-current ratios. A guard band indicating the uncertainty frequencies can be specified for the ins

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ction Network: eaction Network is checked by passing t through the input of the instrument, test ( I), input voltage ( U) and output s frequencies. using the same nput current (input impedance) and fer impedance or network response) are ed from the nominal component values are must be taken in the arrangement of capacitance, lead inductance and ing instrument do not significantly affect nty of measurement at various instrument.

Calibration: Each instrument that is used to determi certification shall be routinely calibrated that no drift of its performance outside t

• ccurred.

Calibration in a confirmation system is c Measurement of input resistance The d.c. input resistance is measured and ideal value, 2 000 ohms. Measurement of instrument performa The input voltage and the output voltage the meter) are measured at various frequen the data in tables as appropriate. The inpu to produce output indications in the range for which the measuring instrument is in

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mine acceptability for the purpose of ted in a confirmation system to ensure de the limits of permissible error has is carried out in two steps. ed and its value is checked against the rmance age (or milli-amperes as indicated on requencies and the ratios compared to he input voltages used should be such as ange of the TOUCH CURRENT values s intended.

Frequency Range of Calibration: In the distant past, touch current was ty driven by line voltage through linear impedan power electronics, switching power supp the touch current available from even the become non-sinusoidal. Fourier expansion of non-sinusoidal tou fundamental frequencies of 50 and 60 H

• rder frequency components that must

important to ensure that touch current m measure current not only the fundamen the higher frequency components conta form. Depending upon the electronic circuitry possible to generate lower frequencies Therefore, capability to measure lower important.

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typically sinusoidal 50 or 60-Hz current

• impedance. With the introduction of

upplies and other electronic circuitry, the most ordinary products has touch current wave forms with 60 Hz, results in many significant higher st be measured. Therefore, it is t measuring instruments can accurately ental power line frequency but also at

• ntained in the non-sinusoidal wave

try in the product under test, it is also es than the mains power frequency. er frequency touch currents is also

References: Shown on the slide are three of the main re

• presentation. Additionally, I visited a large

to tabulate here.

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references used to prepare this rge number of Internet Sites too numerous