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