CURRENT RAMPING
Basics of Magnetism
• The atomic force that can
attract or repel through
space, air, solid matter.
• An invisible field (Flux)
exists between the poles
of a magnet
• This field can be used to
act upon ferrous (iron)
materials
• Even without direct
contact, magnets can
influence ferrous objects
Basics of Magnetism
• Each magnet has
a north & south
pole
• Like poles repel
• Unlike poles attract
Magnetic Flux
• Invisible magnetic field is called Flux
Electromagnetism
• Interaction between
electricity & magnetism
• When electricity flows
through a wire, a
magnetic field is setup
around the wire
• This field is weak, but
can be detected by
certain test equipment
Electromagnet
• Wrapping a nail with
copper wire, passing
current through the
wire, magnetizes the
nail
• The more wire &
more current, the
stronger the magnet
field
Electromagnetic Induction
• A wire carrying electricity
produces an electrical
current in an other wire.
• The flux around the current
carrying wire induces a tiny
electrical current in the
second wire
• Passing a wire through a
magnetic field will induce a
voltage in the wire.
• The flux will act upon the
free electrons in the wire to
produce electricity
Ignition Coil
How a Current Probe Works
• The strength of the
magnetic field around a
wire depends on the rate of
current flow
• This magnetic field induces
a voltage within the probe
tip.
• The voltage is converted to
DC and amplified.
• The stronger the magnetic
field the higher the voltage
output from the probe.
Why use a Current Probe?
• With a DMM, the circuit must be opened & the
meter inserted into the circuit
• With a current probe the circuit does NOT have to
be disturbed!
• DMM’s only give a numeric value
• Current probes when used with a scope, give a
graphic presentation of what is going on in a
circuit
High Current Probe
• Measures circuits of
0 – 600 A
• For every millivolt
displayed on meter,
is equal to One Amp
( .250v = 250A)
• Used for measuring
large currents such
as starter draw
Low Current Probe
• Measures circuits of 0 – 60 A
• Two settings:
– 1mV/10mA (100mV = 1A) –
used for low current testing
(max 10A)
– 10mV/100mA ( 10mV = 1A)
– Used for high current
testing (max 60A)
Here’s How it Works
• Scopes measure
voltage not current
• Current probes
measure current &
convert to voltage
signals
• Simply clamp probe
around circuit being
tested
• Either wire will work,
remember current is
the same through out
the circuit
The Basics
• Turn on probes, making sure battery is good
• Connect probe to scope, select scale to be used,
zero probe before it is clamped to wire
• Clamp probe around around wire w/ arrow in
direction of current flow
• 10 mV Scale – for every 10 millivolts displayed
on screen equals 1 amp
• 100 mV Scale – for every 100 millivolts on screen
equals 1 amp
Current Ramping
• Gives a true picture of
what is going on with
in a circuit.
• In this circuit we see a
gradual ramping of
current as the injector
is turned on.
• It indicates peak
current & the shift to
current limiting during
the hold period
Ramp Time
• Is the time in milliseconds to
reach peak current flow
• In this illustration the current
limiting section shows that
the IC module can regulate
max current to a safe &
effective level.
• This test measures the coil
dynamically & can help
isolate a defective IC
module
• We can also determine high
resistance, low voltage &
ground issues
Simple Measuresmensts
• Current ramping a fuel
pump circuit is the
easiest and most
effective way to look at
the condition of a fuel
pump
• Clamp probe where
ever convenient
Fuel Pump Specs