“Whether you are using general purpose counters on a test bench or in an automated test system, you want to get data as fast and accurate as possible. There are a few things you can do to speed up the testing process. Today’s counters can Display histograms and trend graphs on the front Panel, helping you gain insight into your design faster on the bench and get test results faster. The bus speed boost also improves test system throughput, and various built-in features give you higher resolution and faster test speeds.In various application areas such as crystal oscillator design and test, ceramic resonator test, data communication system test and radar verification test
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Whether you are using general purpose counters on a test bench or in an automated test system, you want to get data as fast and accurate as possible. There are a few things you can do to speed up the testing process. Today’s counters can Display histograms and trend graphs on the front panel, helping you gain insight into your design faster on the bench and get test results faster. The bus speed boost also improves test system throughput, and various built-in features give you higher resolution and faster test speeds. Faster frequency and time measurements are extremely important in a variety of application areas, such as crystal oscillator design and testing, ceramic resonator testing, data communication system testing, and radar verification testing. Today you’ll learn how to speed up frequency and time measurements using generic counters.
Keysight counters
Snapshot: Testing a Crystal Oscillator
A well-known crystal oscillator manufacturer intends to expand its production line and increase test throughput. They have many test benches, each of which contains multiple single-channel counters. By using the dual-channel Keysight 53230A general-purpose frequency counter/timer, the test engineer more than doubled the throughput on each test bench, relying on the parallel measurement capability of the two channels. In addition to increasing the number of channels, the following factors can also improve throughput: choose the shortest possible gate time within the required number of bits of test resolution; use appropriate settings such as auto level, front panel display, and data transfer.
Faster insight into product designs with on-bench counter measurements
When you measure with the counter on the bench, you first need to select the correct instrument settings for the signal being measured. Being able to view signal information on the counter front panel will increase your confidence that your measurements are set up correctly. For example, the input signal voltage peak-to-peak, minimum and maximum values displayed on the front panel of the counter can help you select the correct input range and trigger level.
The Keysight 53200A Series Universal Frequency Counter/Timer’s front-panel graphical display will further help you visualize the measured data. For example, the Keysight 53230A gives you a choice of trend and histogram display. Trend charts show how measured data has changed over time, while histograms show how the data is distributed. Trend graphs help you quickly identify drifting signals by showing the direction and magnitude of drift. It also gives you information on how fast the resulting drift is. See Figure 1.
Figure 1: Trend Graph of the 53230A Counter
The histogram shows you the distribution of the noise signal. If the noise is Gaussian as you expect, the measurement is working properly. If an unexpectedly high percentage of measurements occur at a certain frequency, there is an unintended modulation effect on the signal, and you need to track down this modulation source. See Figure 2. If the counters don’t have graphics capabilities, you must first detect the potential problem, then configure the test to collect large amounts of data, return the data to the computer, and then use the computer to analyze the data. And now that all of these features are built into the counters, you can use the new counters on the bench to gain faster insight into design product metrics and save a lot of testing time.
Figure 2: Histogram of the 53230A counter
Take faster system measurements
When you use a counter in an automated test system, the total time to obtain a reading can be divided into two major parts: bus exchange time and measurement time. The bus exchange time can also be divided into two parts: the time it takes for the command to configure the measurement, and the time it takes for the command to transfer the measurement back to the computer. Over the past few years, test instrument designers have significantly reduced bus exchange times. The latest Keysight counters have bus communication speeds approximately 100 times faster than previous generation counters, process program commands faster, and return measurements to the computer in less time. Given that the latest counters have drastically reduced bus exchange times, the main factor affecting the speed of frequency readings is measurement time. To reduce measurement time, you can do the following:
C Choose the correct gate time
The most obvious way to speed up counter measurements is to choose the smallest gate time while maintaining the required number of bits of test resolution. The longer the gating time, the higher the number of bits of resolution that can be obtained, but obviously the longer it takes. Modern countdown counters employ techniques that increase the number of bits of resolution while avoiding a proportional increase in gate time. For example, if the counter uses a 10 MHz reference oscillator, the reference itself will have 7 bits of resolution in a 1 s measurement time. By applying resolution enhancement techniques, a 10 MHz clock can produce 10 bits of resolution. Therefore, it is necessary to carefully check the technical indicators of the counter, and select the corresponding gating time according to the required resolution digits.
C uses the fastest interface
Some counters provide various interfaces to the PC. For example, the Keysight 53200A series counters have LAN, USB and GPIB interfaces as standard. If speed is a key requirement for your application, you should choose the fastest interface. Both single measurement and block read throughput are affected by your choice of interface. See Table 1 and Table 2 for details.
Table 1: Keysight 53230A Single Measured Throughput Rates Based on Interface Type and Data Transfer Command
Table 2: Keysight 53230A Counter Fast Reading Throughput Rates Based on Interface Type and Data Transfer Command
C Select the correct command to transfer the measurement data back to the PC
Your counter may provide several ways to transfer data back to the PC. Different methods may have different data transfer rates. Table 1 and Table 2 show the throughput of 53230A, it can be seen that the data transfer command has an impact on the read rate. Therefore, if a large number of readings are to be taken and the total measurement time is minimized, the fastest method of transferring data to the PC should be selected.
C Turn off auto level
Autolevel is a function that automatically determines the trigger level used for the measurement. The counter measures the minimum and maximum voltages of the input signal, calculates the peak-to-peak voltage, and then sets the trigger level to 50% of the peak-to-peak value. Of course, doing these things takes time. To eliminate the time spent automatically finding the trigger level, if you know the signal conditions, you can set the trigger level yourself. It is to turn off the auto level function and set the trigger level to the desired value.
Measurement Skills
You can set the auto level to “ONCE”. This will set the counter to perform the auto-level function once and then disable the auto-level function. Use this method when you don’t know how to set up a measurement trigger, but want to never change the settings once they’re set. The counter will now determine the trigger setting and carry over to this setting for subsequent measurements. Doing so saves measurement time because autolevel is only used once.
C Turning off the front panel display Turning off the front panel display of some instruments can help speed up measurements. A number of tasks are offloaded from the internal microprocessor’s time, including performing measurements, processing bus communications, and providing information for front panel displays. If the display is turned off, the processor can spend all its time measuring and processing data. For example, with the front panel display on, the Keysight 53230A counter can perform 75,000 frequency measurements in 1.35 s and save the measurement results to internal memory. And when the display is off, it only takes 1.22 s to complete the same task. Since the measurement time is mainly determined by the selected gate time, the time spent in the AC portion of the bus is not affected by the display state. However, the counter must process the measurement data internally and save the result to memory. These functions consume internal processor time, so turning off the display can speed up data processing.
Measurement Skills
In order to shorten the total measurement time, the same measurement items should be grouped as much as possible. For example, perform all frequency measurements first, and then perform all period measurements, rather than changing the measurement type for each measurement, while minimizing range and trigger level changes. Time to change measurement configuration – 53200A Series counters typically take 50 ms. C Turning off the front panel display Turning off the front panel display of some instruments can help speed up measurements. A number of tasks are offloaded from the internal microprocessor’s time, including performing measurements, processing bus communications, and providing information for front panel displays. If the display is turned off, the processor can spend all its time measuring and processing data. For example, with the front panel display on, the Keysight 53230A counter can perform 75,000 frequency measurements in 1.35 s and save the measurement results to internal memory. And when the display is off, it only takes 1.22 s to complete the same task. Since the measurement time is mainly determined by the selected gate time, the time spent in the AC portion of the bus is not affected by the display state. However, the counter must process the measurement data internally and save the result to memory. These functions consume internal processor time, so turning off the display can speed up data processing.
in conclusion
Whether you’re measuring on the bench or in an automated test system with a general-purpose counter, you can gain faster insight into your design by reducing total test time by selecting counter features and employing a variety of techniques. On the bench, the time to insight into design performance can be accelerated through the front panel display of characteristics such as the voltage and trigger information of the input signal.
Front panel trend and histogram displays help you get a quicker understanding of the measurements you’re making. You can also achieve faster system measurements by choosing the correct interface and data transfer method, as well as appropriate parameter settings such as gate time, auto level, and front panel display settings. If you frequently perform frequency measurements, Keysight counters will provide you with fast, stable, and accurate measurements you can count on.
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