When performing functional tests, keeping test times as short as possible is often a critical requirement. Time is money, after all. One way to reduce test times is to reduce the latency in setting up signal switch paths, stimulus devices, and measurements. These can all have a significant impact on the overall time it takes to complete a full functional test of a particular DUT.
One way to reduce the latency introduced by using the host PC to control switch closures is to use a feature called scanlists when using VTI Instruments' VXI bus instruments, such as the VM2710 DMM and SMIP family of switching products. This feature allows users to pre-load the SMIP switches with a list of relays to be opened or closed when triggered. Similarly, users can pre-load the VM2710 DMM with a list of channels to be measured.
Using this feature, the host PC does not individually command relays to open and close. Instead, a hardware trigger commands multiple relays to open and close simultaneously. Once the relays have settled, the DMM is triggered to make the measurement. The process is as follows:
- DMM Setup (1 communication transaction from PC)
- Trigger System Setup (1 communication transaction from PC)
- Load Scanlist (1 communication transaction from PC)
- Initiate Scan (1 communication transaction from PC)
- Switch Closure. Once relays settle, trigger is sent to DMM.
- DMM takes a measurement. Once measurement is complete, a trigger is sent to the switch.
- Repeat steps 5 and 6.
The time saved with this approach is directly related to the number of channels that need to be measured. For example, if a total of 500 channels need to be measured, a well-planned routine can turn 504 communication transactions from the PC into only 4, thus greatly reducing overall test time.
A similar process can be used to reduce test times when using the EX1200 Series High-Density Switch/Measure and Control Systems. In addition to being able to include switch closures in the scanlist, the EX1200 provides an interface to include DMM and stimulus setup as part of the scan. For tests that require the DMM to perform multiple measurements, this is a valuable feature. The process is as follows:
- Load scanlist (1 communication transaction)
- Initiate scan (1 communication transaction)
- Switch closure. Once relays settle, trigger is sent to DMM.
- DMM takes a measurement. Once measurement has been completed, a trigger is sent to the switch.
- Repeat steps 3 and 4.
- DMM receives a separate trigger instructing it to change measurement function. Once the measurement is complete, a trigger is sent to the switches.
- Switch closure. Once the relays settle, a trigger is sent to the DMM.
- DMM takes a measurement. Once the measurement is complete, a trigger is sent to the switch.
- Repeat steps 6-8.
Using this approach, a test consisting of thousands of channels and many different measurement types can be completed in the in the shortest time possible, virtually independent of a host PC.
For more information, contact an authorized AMETEK Programmable Power sales representative in the United States by visiting https://www.vtiinstruments.com/sales/vti-instrument-sales. AMETEK Programmable Power also can be contacted directly toll free at 800-733-5427 or 858-450-0085 or at firstname.lastname@example.org.