DIGITAL MULTIMETER TEST ENVIRONMENTS

While digital multimeters are still commonly used in benchtop testing, there are now a number of interconnect options for system integration; e.g., some multimeters offer hobbyists and engineers alike USB interfaces and general purpose interface buses for control via PC using test commands. Certain LabVIEW drivers allow one to integrate one’s multimeter into a larger test system. Then there are front-panel thermocouple inputs which allow one to connect directly to many prevalent temperature measurement sensors.

Indicating a multimeter’s susceptibility to noise, digital multimeters have specifications for normal mode rejection ratio and common mode rejection ratio with common values of over sixty decibels and one hundred twenty decibels. The noise produced by one’s multimeter is particularly important when measuring low signal levels, and electromagnetic interference standards influence compliance levels.

Because of its influence on throughput, a digital multimeter’s measurement speed — typically displayed as readings per second at a specific resolution level — is especially important in production environments.

A number of modern multimeters have resolution levels that one can program, thus simplifying balancing speed and accuracy. The integration period, which is the amount of time when a signal is sampled by the multimeter’s analog-to-digital convertor, is typically displayed in number of power line cycles; number of power line cycles made up of integer multiples — one, five, ten, etc. — will reduce the fifty/sixty hertz line pickup, which is the most common type of noise. One will have greater noise reduction with a larger number value with the caveat that measurementS will take longer to complete.

The number of analog-to-digital conversions averaged for each reading, or digital filtering, can stabilize readings with excess noise but, again, this will slow measurement times.

One’s multimeter measures internal voltages in order to retain stability and accuracy with temperature changes over time when a multimeter’s autozero is used, but overuse of autozero will negatively impact the multimeter’s reading rate. Throughput can be increased by disabling autozero, performing it at certain intervals, or programming the multimeter to use autozero during the load/unload cycle.

Speed specifications like range changing speed, autorange time, and function changing rate might also affect throughput, and hardware triggers are generally faster than software triggers. Certain digital multimeter’s have a microprocessor dedicated to triggers which can significantly reduce latency. Setting or response time is also important when one is testing high-impedance devices.

Speedy and accurate switching is notably important in production test environments, because hundreds or even thousands of devices have to be tested every shift, and newer models support hundreds of multiplexer channels or thousands of matrix crosspoints.

PRINTED CIRCUIT BOARD MATERIALS & APPLICATIONS

Using different printed circuit board (PCB) materials will result in different circuit board specifications and prices with regard to PCB prototyping and production. Certain one- or two-layer boards need what is known as pre-preg core — which is a material made from fine layers of fiberglass that is pre-impregnated with a bonding agent or metal core — or several layer boards using two or more kinds of cores for construction. Board thickness varies from a few millimeters thick, for flexible boards, to as much as a quarter inch thick, for heavy burn-in boards. Core materials typically resemble thin double-sided boards with dielectric materials (e.g. fiberglass) as well as copper foil on each side, and they generally come in predetermined thicknesses.

FR4 is the most commonly used type of substrate for circuit boards and is made from a glass-fiber epoxy laminate. FR4 has higher temperature coefficients and lower dielectric constants — e.g. FR4 has a starting thermogravimetry (TG) of one hundred forty degrees Celsius, FR4-06 has a TG of one hundred seventy degrees, and the temperature increases as the family number increases.

Prototypes using metal core, which has impressive heat elimination, are quite popular for light emitting diode (LED) circuit boards. The metal core is an efficient heat sink and keeps the LEDs operating at safe temperatures. One section of a metal core printed circuit board prototype has a metal base, a non-conductive layer (usually aluminum), a copper circuit layer, integrated circuit (IC) components, and a solder mask.

Polyimide printed circuit board prototypes, which are tougher than FR4, can sustain significantly hotter temperatures, making them perfect for most electrical insulation applications. The polyimide is made up of a silicone adhesive and a polyimide film designed to withstand higher temperatures and will protect edge connectors, gold edge fingers (during wave soldering), and reflow soldering (during circuit board assembly). Polyimide can be distinguished from other boards by its distinctive brown color.

Polytetrafluoroethylene (PTFE) or woven glass base circuit board materials necessitate special drilling procedures because Teflon is much softer than, e.g., FR4. These types of materials are far more common than they once were. PTFE/woven glass base materials provide rapid growth of applications operations and easily meet high-frequency demands, and they consistently perform well.

You can also use Arlon materials for longer operating lives at high temperatures, or Isola range circuit board prototypes for broadband circuit designs requiring faster signal speed or better signal fidelity.

USING AN OSCILLOSCOPE ON AUTOMOBILES

A digital storage oscilloscope makes it easy to visualize alternating current electrical signals in an automobile. Oscilloscopes have several electrical inputs and control knobs as well as a liquid crystal display (LCD) screen for displaying the signal.

Generally automotive oscilloscopes are used in manufacturing applications by engineers to set electrical signals to the right form. They are also frequently used in garages by mechanics to test the engine’s components for faults. In addition oscilloscopes are increasingly being used by do-it-yourselfers and those looking to make their own automotive repairs. Some examples of electrical signals that one might observe with an oscilloscope are the ignition sequence and the throttle position sensor’s output.

Let’s take a look at how you can use your oscilloscope on your automobile.

Step One

First you’ll need a coaxial cable, which you will connect between the car’s output that you are testing and one of the oscilloscope’s inputs. Most simple digital storage oscilloscopes have two inputs, typically labelled A and B. It doesn’t matter which input you use. You’ll switch the input on by, e.g., pressing either the A or B button.

Step Two

Next you’ll alter the volts/division control in order to change the vertical scale as well as the number of volts for each division. You won’t be able to see the electrical signal clearly on your oscilloscope’s display  until you’ve adjusted the settings appropriately.

Step Three

Now it’s time to adjust the oscilloscope’s time/division (also known as timebase) control which changes the number of times each horizontal division is shown. When you know the electrical signal’s frequency you can accurately calculate the time/division. The time for a single period is T=1/f (with f being the frequency). Then you’ll set the time/division to the calculated value using the equation above.

Step Four

The last step is to adjust the vertical position control, which will move the signal up or down on the oscilloscope’s display. Your goal is to center the signal.

By following these four simple steps you can use your digital storage oscilloscope to observe your automobile’s electrical signals.