Fluke 87V-MAX Product Manual - Page 27

Continuity Testing, Measuring Resistance

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87 Users Manual To calculate the burden voltage: in A, multiply the display reading by 0.03V; in mA, multiply the display reading by 1.8 mV; in µA, multiply the display reading by 100 µV. For example, at a 20 mA display reading, the burden voltage is 20.00 x 1.8 mV = 36 mV. The approximate resistance between the input terminals is 0.03 ohms for A, 1.8 ohms for mA, and 100 ohms for µA. Continuity Testing Continuity testing verifies that circuit connections are intact. To perform audible continuity tests, set the rotary switch to ReE press T and connect the meter to your circuit. Test resistances below the values listed in Table 3 cause the meter to emit a continuous tone. Use the 400 ohm range for most wiring checks. The continuity mode is extremely fast and can be used to detect either shorts or opens that last for as little as 1 millisecond. When a change is detected, the beeper tone is "stretched" to last at least 1/4 second so you can hear it and detect both shorts and opens. This can be a valuable troubleshooting aid when looking for intermittents associated with cables, connections, switches, relays, etc. If the test value is very close to the threshold, erratic beeps can also occur due to environmental electrical noise (EMI). 20 Measuring Resistance Caution Turn off power on the test circuit and discharge all capacitors before attempting incircuit resistance measurements. If an external voltage is present across a component, it will be impossible to take an accurate measurement of the resistance of that component. The meter measures resistance by passing the same current through a precision reference resistor and the external circuit or component, then ratios and measures the voltage drop across each (Ω = Vunknown/ Vreference). Remember, the resistance displayed by the meter is the total resistance through all possible paths between the probes. This explains why in-circuit measurement of resistors does not often yield the ohms value indicated by the resistor's color code. The resistance in the test leads can diminish accuracy on the lowest (400-ohm) range. The error is usually 0.1 to 0.2 ohms for a standard pair of test leads. To determine the error, short the test leads together and read the resistance of the leads. Use the Relative (REL) mode to automatically subtract the lead resistance from resistance measurements. MyFlukeStore Find QuaSlhitoypPforordFulucktespOrondliuncetsato:nline awt:ww.wGwlo. balTestSupply.com.com [email protected]

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87
Users Manual
20
To calculate the burden voltage: in A, multiply the display
reading by 0.03V; in mA, multiply the display reading by
1.8 mV; in
μ
A, multiply the display reading by 100
μ
V. For
example, at a 20 mA display reading, the burden voltage
is 20.00 x 1.8 mV = 36 mV.
The approximate resistance between the input terminals is
0.03 ohms for A, 1.8 ohms for mA, and 100 ohms for
μ
A.
Continuity Testing
Continuity testing verifies that circuit connections are
intact. To perform audible continuity tests, set the rotary
switch to
ReE
press
T
and connect the meter to
your circuit. Test resistances below the values listed in
Table 3 cause the meter to emit a continuous tone. Use
the 400 ohm range for most wiring checks.
The continuity mode is extremely fast and can be used to
detect either shorts or opens that last for as little as 1
millisecond. When a change is detected, the beeper tone
is "stretched" to last at least 1/4 second so you can hear it
and detect both shorts and opens. This can be a valuable
troubleshooting aid when looking for intermittents
associated with cables, connections, switches, relays, etc.
If the test value is very close to the threshold, erratic
beeps can also occur due to environmental electrical
noise (EMI).
Measuring Resistance
Caution
Turn off power on the test circuit and
discharge all capacitors before attempting in-
circuit resistance measurements. If an
external voltage is present across a
component, it will be impossible to take an
accurate measurement of the resistance of
that component.
The meter measures resistance by passing the same
current through a precision reference resistor and the
external circuit or component, then ratios and measures
the voltage drop across each (
Ω
= Vunknown/
Vreference). Remember, the resistance displayed by the
meter is the total resistance through all possible paths
between the probes. This explains why in-circuit
measurement of resistors does not often yield the ohms
value indicated by the resistor’s color code.
The resistance in the test leads can diminish accuracy on
the lowest (400-ohm) range. The error is usually 0.1 to 0.2
ohms for a standard pair of test leads. To determine the
error, short the test leads together and read the resistance
of the leads. Use the Relative (REL) mode to
automatically subtract the lead resistance from resistance
measurements.
Shop for Fluke products online at:
1.888.610.7664
www.
MyFlukeStore
.com