The Pioneer of Modern Leak Testing

Leak Test Steps in “Zero-Time”

“Uh-Oh, what could this possibly be about?” you might be wondering. There can’t be any such thing as “zero-time”.

Well, strictly speaking you are right, but there’s a neglected feature in the Optima leak tester that we couldn’t think of a better name for.

The Uson Optima vT is designed to be accurate and reliable, but at the same time FAST. This is why it has multiple high-resolution sensor inputs that are sampled simultaneously. The Optima vT can make accept/reject decisions in a short period of time. Most applications require more than a simple accept/reject decision though and it is usually also necessary to log the sensor data that led to the decision.

Stay with me while I attempt to explain how this handy little feature works and how it just might take your leak testing to another level………

A long time ago, Uson came up with the concept of breaking the leak test into multiple “steps” that are named and numbered. Not only does this simplify the test program, it allows customization, and provides the option of logging a result for each step. This is where zero-time steps are handy.

Say, for example, that four different volumes need to be flow or leak tested concurrently over the same 2 second period. With Optima vT, a 2-second “timed” step can take the sensor measurements; then four zero-time steps can calculate the leak rate and make the accept/reject decisions for each volume. No cycle time increase! But the log file will plainly show the data and decision result for each volume’s zero-time step. In a nutshell, a zero-time step inherits sensor data from a preceding “timed” step and then executes as part of that step. Now that IS clever!

There are numerous uses for zero-time steps. Here are just a few more:

    • Combination Leak/Occlusion test where adjacent chambers are simultaneously tested. A timed step checks the leak rate for one chamber using sensor #1. A zero-time step checks sensor #2’s result to make sure there was no pressure build-up in the adjacent chamber. The log file would have results for each chamber in separate steps.
    • Sometimes a zero-time step is useful even if only one sensor is used. For example, if you need to grade the part at run time, multiple back-to-back zero-time steps can each have separate limits ranges allowing different outputs to be turned on in each zero-time step. This facilitates marking or routing the part under test.
    • Even though Optima vT supports multiple limits per step, it is sometimes beneficial to put each limit in a zero-time step just to simplify the log file.
    • Optima vT’s test programs are highly customizable to fit the application. It is sometimes necessary to jump to a different step or program depending on a limit comparison result. A zero-time step can make the decision to transfer program execution without adding to the overall cycle time.
    • Many years ago, Uson developed the Pressure-Decay Leak Testing technique that converts a pressure change to a leak rate. For diagnostic reasons, the plant engineer sometimes wants both the delta-pressure value and the calculated leak rate stored in the log file. A zero-time step allows doing this.
    • Uson’s Temp Comp provides a way to compensate a Pressure-Decay Leak Test for temperature changes. It is sometimes useful to log the leak rate with and without TempComp enabled so that the plant engineer can compare the two results. The zero-time step can do this without increasing cycle time.
    • Optima vT offers a feature called StepMath, which is a math operation that can be done at the end of any step. It is another one of the features that makes Optima vT very flexible. The inputs to the math operation can be sensor data from previously executed steps and constant coefficient data. Since StepMath can act on data from previous steps, it often simplifies the test program to put the operation in a zero-time step.
    • The Optima vT can handle applications that require a short test cycle, but at the same time make lots of pass/fail decisions and log data that led to the decisions. The zero-time step is just one of the tools that Uson uses to accomplish this goal.

The use of zero-time steps is clearly a very powerful and useful tool, and to be honest, it’s one that we haven’t done a great job of explaining in the past. If you would like more information on how to set it up or have a question about a possible application, please don’t hesitate to call and talk to one of our application engineers.

Joe Pustka

Director Applications Engineering

Contact Us


Uson L.P. - Corporate

8640 N. Eldridge Parkway
Houston, TX 77041 USA

Tel: +1-281-671-2000
Fax: +1-281-671-2001


Uson UK – Europe

Western Way
Bury St. Edmunds
Suffolk, IP33 3SP United Kingdom

Tel: +44-1284-760606
Fax: +44-1284-763049


Uson – China

Room 601, 567 Lan Gao Road
Shanghai, 200333, China

Main: 021-583 65859, 021-583 59187
Fax: 021-583 59185, 021-337 73559