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A G R E AT E R M E A S U R E O F C O N F I D E N C E
Shaving Milliseconds
off of Test Time
Mark Cejer
Business Manager, Keithley Instuments, Inc.
Cleveland, OH
T
HE concept of a test sequencer is urement. Data is then sent from the instru- a significant communications bottleneck by
not entirely new. Essentially a ment to the PC where the PC decides wheth- enabling the instrument to communicate di-
sequential list of test operations er the DUT (device under test) is in tolerance rectly with the handler. The test sequence is
that reside outside the PC, test se- or not. If it is out of tolerance, the PC sends downloaded to the instrument from the PC,
quencers have been readily avail- a signal to the handler to reject the part and which is a one-time event. When the device
able in higher-end ATE systems that can cost another test can begin. handler places a part into position, it sends
upwards of a million dollars. Now, test se- The main problem with this type of setup a signal to the instrument to begin the test.
quencers are becoming more common in less is the slow and continuous communication The instrument performs the test, makes the
expensive instruments as well. Here's a look of data between the PC and the instrument. pass/fail decision, and sends instructions
at how test sequencers can speed up tests on The test sequencer approach, on the other back to the handler. This eliminates the con-
optical devices, saving time and money. hand, involves a connection from the PC tinuous transfer of data over GPIB and there-
A test sequencer is essentially a sequential to the instrument and from the instrument fore decreases test time.
list of test operations that a system performs to the device handler. Eliminating the link In most cases, an improvement in over-
on a device. Test sequencers are preloaded from the PC to the device handler removes all test throughput of as little as 10 to 100
into a test instrument, saving the instrument
and the device handler from having to com-
municate continuously with the PC. This au- Component Handler
tomates the test process and shaves precious
time off of the test cycle. Digital I/O Mechanical
In a typical test setup without test se- Connection
quencing, a PC communicates with a test in-
IEEE-488 Test Test Leads
strument via an IEEE-488 (GPIB) link and PC DUT
Instrument
with a part handler through a serial link. The
PC receives a signal from the parts handler
Test Fixture
indicating that a component is in place and
that the test can begin. The PC then sends a Figure 1. In a typical production test setup, a test sequencer residing in the instrument eliminates a
command to the instrument to make a meas- link between the PC and the component handler, speeding up the test process.
Shaving Milliseconds off of Test Time February 2005 1
milliseconds per part has a direct impact units can slow down more sensitive meas-
on the cost of test and therefore the overall urements and speed up others to optimize About The Author:
profitability of a manufacturing line. Not overall timing. Mark Cejer is a Business Manager for
only that, the quantity of products shipped The traditional barrier for smaller man- Keithley Instruments, where he is respon-
goes up because testing is quicker, therefore ufacturers or those with higher mix/ lower sible for developing Precision Electronic
helping a manufacturer add capacity without volume products, or startups, has been the Test applications, markets, and products.
investing additional capital. cost of test systems. Test systems based on Mark has been with Keithley for over 10
Instruments with test sequencers can run instruments and test sequencers can now be years and during that time has led the
up to 100 complete test sequences without developed, deployed, and operated for typi- launch of the Keithley SourceMeter