♪ AC ♪ ♪ Electricity ♪ DC ♪
Today we're demonstrating a new design tool--
a Web app that allows you to calculate
the magnetic field from a circuit-board trace,
and the output from a magnetic sensor.
Here's the diagram.
The app lets you define:
the PC board thickness;
copper thickness;
the trace width;
the current through the trace;
the type of sensor;
and the sensor supply voltage.
We can also select zero board thickness,
for the trace on the top side of the board.
We'll select a 0.09-inch, 2.3 millimeter trace,
and one-ounce copper.
We'll enter 10 amps.
There's a warning that the current exceeds the trace guideline
for a 30 degree temperature rise.
So we'll change to two-ounce copper.
Let's choose an AA003-02 sensor,
which is popular for current-sensing...
...and a nine-volt supply.
The predicted output is 392 millivolts.
Let's see how that corresponds to an actual measurement.
We cut off sensor pins 2, 3, 6, and 7
to allow room for the trace on the top side of the board.
The sensor is powered by a nine-volt battery,
and connected to an oscilloscope.
The yellow 'scope trace is the signal generator;
cyan is the sensor output.
We ramp plus/minus 10 amps through the trace.
The output is 440 millivolts,
which agrees with the model
to within the sensor's sensitivity specification range.
Here's how the app works:
For narrow traces, the field can be approximated
by Ampere's law.
But the approximation breaks down for wider traces,
which are needed for higher current.
So the app does finite element analysis,
breaking the trace into an array of thin traces.
So to sum up, this app makes it easy to design noncontact current sensing.
The advantages of this type of sensing are:
a wide current range;
negligible insertion resistance;
measurement down to dc;
and inherent electrical isolation.
Here's the URL.
Click, e-mail, or call us for more information, or to order parts or evaluation kits.