Touch Current Basicsprepared for CTL PTPWorkshop May 2010

Ronald VaickauskiSenior 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 1Values 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 engineering at the University of California Berkley, did research on human response to electric shock and wrote a book, “The Effect of Electric Shock on Man.” Much of the requirements in place for touch current are based on his work.

Another major contributor was Walter E. Hart, Fluke Corporation who was a member of the IEC 66E committee and IEC TC 74 Working Group 5.

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Charles F. Dalziel, a professor of electrical engineering at the University of California Berkley, did research on human response to electric shock and wrote a book, “The Effect of Electric Shock on Man.” Much of the requirements in place

Another major contributor was Walter E. Hart, Fluke Corporation who was a member of the IEC 66E committee and IEC TC 74 Working Group 5.

Perception/Reaction Findings:

Perception/reaction current flowing through the body is just enough to cause involuntary muscular contraction to the person through which it is flowing

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Perception/reaction current flowing through the body is just enough to cause involuntary muscular contraction to the person through which it is flowing

Let-Go Findings:

Let-Go current flowing through the body is just enough to cause involuntary contraction of a muscle, such as inability to let gofrom an a.c. electrode.

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current flowing through the body is just enough to cause involuntary contraction of a muscle, such as inability to let go

Ventricular Fibrillation:

Ventricular fibrillation current flowing through the body is just enough to cause ventricular fibrillation of the heart. human heart is in danger of failure to function.

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current flowing through the body is just enough to cause ventricular fibrillation of the heart. Ventricular fibrillation is where the human heart is in danger of failure to function.

Elementary Touch Current Network:

The three component combination of the 500 parallel combination of the 1500Ω resistor and 0.22 the body impedance model. It represents handelectrical impedance of a person touching a conductive part. The 1500 resistor in parallel with the 0.22 µF capacitor represents the combined impedance of the entry and exit skin contacts (wet skin, not immersed) with a conductive surface of equipment and ground, or with two equipment contacts. The 500Ω resistor represents the internal body resistance, less the skin, and serves as the current-sensing resistor in the measuring circuit since all of the current that flows through the body impedance model flows through this resistor.

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The three component combination of the 500 Ω resistor in series with the resistor and 0.22 µF capacitor comprises

the body impedance model. It represents hand-to-hand or hand-to-feet electrical impedance of a person touching a conductive part. The 1500 Ω

F capacitor represents the combined impedance of the entry and exit skin contacts (wet skin, not immersed) with a conductive surface of equipment and ground, or with two equipment

resistor represents the internal body resistance, less the sensing resistor in the measuring circuit

since all of the current that flows through the body impedance model flows

Threshold of Perception:

The human bodies response to touch current varies with frequency. The threshold of perception increases with frequency. The graph shown is figure 1 of IEC 60479-2:2007.

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The human bodies response to touch current varies with frequency. The threshold of perception increases with frequency. The graph shown is figure 1 of IEC TS

Perception/Reaction Network:

The touch current network for perception/reaction is a frequency weighted network. This network is the one most often referenced I product safety testing standards. by a voltage-divider consisting of the resistor and capacitor connected across the 500 current-sensing resistor. The frequency-weighting network is essentially a lowdesigned to attenuate the voltage signal from the 500 of the body current. The voltage transfer characteristics of the network is designed from Dalziel's data describing human responses for perception or startle reaction.The frequency weighting network causes the instrument to have an indication that is related to the expected level of physiological response, independent of frequency. A touch current measuring instrument is not a substitute for an ammeter. The touch current measuring instrument's response is not necessarily equal to the number of millithrough the body impedance model. The reading of a touch current measuring instrument is adjusted by the frequency-weighting network for variations in human response due to frequency. Therefore, the reading can be compared to the limit value in the requirements without knowing the frequency, and allowing a single numerical value for the touch current limit for the physiological effect to be addressed.

Actual RMS current measured through the 500 Weighted current indicated by the voltage after the reaction is related to the body muscular response to the touch current independent of frequency. Weighted current is useful to evaluate current comprised of combinations of frequencies, including nonshapes. The weighted current is referenced to the 50/60physiological effect.

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The touch current network for perception/reaction is a frequency weighted network. This network is the one most often referenced I product safety testing standards. The frequency-weighting is done

divider consisting of the resistor and capacitor connected across the 500 Ω weighting network is essentially a low-pass filter

designed to attenuate the voltage signal from the 500 Ω resistor according to the frequency of the body current. The voltage transfer characteristics of the network is designed from Dalziel's data describing human responses for perception or startle reaction.The frequency weighting network causes the instrument to have an indication that is related to the expected level of physiological response, independent of frequency. A touch current measuring instrument is not a substitute for an ammeter. The touch current measuring instrument's response is not necessarily equal to the number of milli-amperes flowing through the body impedance model. The reading of a touch current measuring instrument is

weighting network for variations in human response due to frequency. Therefore, the reading can be compared to the limit value in the requirements without knowing the frequency, and allowing a single numerical value for the touch current limit for the physiological effect to be addressed.

Actual RMS current measured through the 500 Ω resistor relates to electrical burns. Weighted current indicated by the voltage after the reaction is related to the body muscular response to the touch current independent of frequency. Weighted current is useful to evaluate current comprised of combinations of frequencies, including non-sinusoidal wave shapes. The weighted current is referenced to the 50/60-Hz current that produces a certain

Let-Go Network:

The touch current network for “let-go” is also a frequency weighted network. voltage transfer characteristics of the network is designed to emulate human responses for the “let-go” response.The frequency weighting network causes the instrument to have an indication that is related to the expected level of physiological response, independent of frequency. The reading of a touch current measuring instrument is adjusted by the frequencyhuman response due to frequency. Therefore, the reading can be compared to the limit value in the requirements without knowing the frequency, and allowing a single numerical value for the touch current limit.

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go” is also a frequency weighted network. The voltage transfer characteristics of the network is designed to emulate human

The frequency weighting network causes the instrument to have an indication that is related to the expected level of physiological response, independent of frequency. The reading of a touch current measuring instrument is adjusted by the frequency-weighting network for variations in human response due to frequency. Therefore, the reading can be compared to the limit value in the requirements without knowing the frequency, and allowing a single numerical value for the touch current limit.

Calculated Impedance Perception/Reaction Network:

The performance of the Perception/Reaction Networkvariable frequency sinusoidal current through the input of the instrument, test terminals A and B. The input current ( I), input voltage ( U) and output voltage ( U2) are measured at various frequencies. using the same voltmeter.

Measured ratios of input voltage to input current (input impedance) and output voltage to input current (transfer impedance or network response) are compared with ideal values calculated from the nominal component values specific. In building the instrument, care must be taken in the arrangement of the circuitry so that inter-component capacitance, lead inductance and characteristics of the voltage measuring instrument do not significantly affect the voltage-current ratios.

A guard band indicating the uncertainty of measurement at various frequencies can be specified for the instrument.

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Calculated Impedance Perception/Reaction Network:

Perception/Reaction Network is checked by passing variable frequency sinusoidal current through the input of the instrument, test terminals A and B. The input current ( I), input voltage ( U) and output voltage ( U2) are measured at various frequencies. using the same

Measured ratios of input voltage to input current (input impedance) and output voltage to input current (transfer impedance or network response) are compared with ideal values calculated from the nominal component values specific. In building the instrument, care must be taken in the arrangement of

component capacitance, lead inductance and characteristics of the voltage measuring instrument do not significantly affect

A guard band indicating the uncertainty of measurement at various frequencies can be specified for the instrument.

Calibration:Each instrument that is used to determine acceptability for the purpose of certification shall be routinely calibrated in a confirmation system to ensure that no drift of its performance outside the limits of permissible error has occurred.

Calibration in a confirmation system is carried out in two steps.

Measurement of input resistanceThe d.c. input resistance is measured and its value is checked against the ideal value, 2 000 ohms.

Measurement of instrument performanceThe input voltage and the output voltage (or millithe meter) are measured at various frequencies and the ratios compared to the data in tables as appropriate. The input voltages used should be such as to produce output indications in the range of the TOUCH CURRENT values for which the measuring instrument is intended.

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Each instrument that is used to determine acceptability for the purpose of certification shall be routinely calibrated in a confirmation system to ensure that no drift of its performance outside the limits of permissible error has

Calibration in a confirmation system is carried out in two steps.

The d.c. input resistance is measured and its value is checked against the

Measurement of instrument performanceThe input voltage and the output voltage (or milli-amperes as indicated on the meter) are measured at various frequencies and the ratios compared to the data in tables as appropriate. The input voltages used should be such as to produce output indications in the range of the TOUCH CURRENT values for which the measuring instrument is intended.

Frequency Range of Calibration:

In the distant past, touch current was typically sinusoidal 50 or 60driven by line voltage through linear impedance. With the introduction of power electronics, switching power supplies and other electronic circuitry, the touch current available from even the most ordinary products has become non-sinusoidal.

Fourier expansion of non-sinusoidal touch current wave forms with fundamental frequencies of 50 and 60 Hz, results in many significant higher order frequency components that must be measured. Therefore, it is important to ensure that touch current measuring instruments can accurately measure current not only the fundamental power line frequency but also at the higher frequency components contained in the nonform.

Depending upon the electronic circuitry in the product under test, it is also possible to generate lower frequencies than the mains power frequency. Therefore, capability to measure lower frequency touch currents is also important.

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In the distant past, touch current was typically sinusoidal 50 or 60-Hz current driven by line voltage through linear impedance. With the introduction of power electronics, switching power supplies and other electronic circuitry, the touch current available from even the most ordinary products has

sinusoidal touch current wave forms with fundamental frequencies of 50 and 60 Hz, results in many significant higher order frequency components that must be measured. Therefore, it is important to ensure that touch current measuring instruments can accurately measure current not only the fundamental power line frequency but also at the higher frequency components contained in the non-sinusoidal wave

Depending upon the electronic circuitry in the product under test, it is also possible to generate lower frequencies than the mains power frequency. Therefore, capability to measure lower frequency touch currents is also

References:

Shown on the slide are three of the main references used to prepare this presentation. Additionally, I visited a large number of Internet Sites too numerous to tabulate here.

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Shown on the slide are three of the main references used to prepare this presentation. Additionally, I visited a large number of Internet Sites too numerous