- September 05, 2017
- Fluke Corporation
By Bill Lydon, Editor, Automation.com
Proper pressure instrument calibration requires the coordination of a number of factors to ensure precise accuracy. Improving this pressure calibration process can really boost an instrumentation team‚Äôs productivity and overall production.
By Bill Lydon, Editor, Automation.com
Pressure measurements are often critical to the quality and efficiency of process control systems. Proper pressure instrument calibration requires the coordination of a number of factors to ensure precise accuracy. Improving this pressure calibration process can really boost an instrumentation team’s productivity and overall production. Fluke has produced a new product, designed to help these professionals streamline calibration, and I sat down with Product Marketing Manager Jim Shields who walked me through the new Fluke 729 Automatic Pressure Calibrator product.
The Four Common Issues of Calibration
As a 25-year industry veteran, Shields understands instrumentation and calibration. He described some of the four most common issues that today’s process technicians encounter when performing pressure calibrations:
1. Slow Leaks
A leaking pressure source makes it difficult to maintain a stable pressure at calibration points long enough to take an accurate reading. Slow leaks can require technicians to constantly fine tune and adjust pressure applied from a pump making it difficult for the system to settle. This complicates the recommended procedure to let the system settle for several seconds or even minutes at the desired pressure set point for a more accurate and repeatable test result.
2. Documenting pressure calibration requires multiple tools
Documenting pressure calibration results is important in order to maintain accurate critical instrument records, but the number of steps associated with documenting the procedure, and the number of tools required for the average pressure calibration can make the task immensely more difficult. For instance, a typical pressure calibration could require a pressure calibrator, pressure module or gauge for measuring pressure, a pump to generate pressure, and multiple hoses and fittings between the devices (including the connections to the pressure transmitter itself).
3. Manually generating and controlling the pressure for each test point
Pressure calibrations in process manufacturing environments rarely require testing to occur at a single test point. In fact, a typical pressure calibration can require anywhere from three to eleven pressure test points. Trying to adjust and fine tune system pressure for these specific points can be difficult and time consuming. Each individual point requires technicians to increase or decrease pressure by either pumping the system up or releasing pressure, and then to fine tune the pressure using the fine adjust Vernier of the test pump. This process can be simplified by spending extra time carefully matching the selected hand pump to the pressure range of the transmitter being tested. For instance, some portable pneumatic pumps have pressure ranges that go up to 600 psi / 40 bar, but it can be difficult to accurately increase pressure beyond 400 psi / 28 bar. There are, however, newer portable pumps that can be easily pumped and adjusted to over 1,000 psi / 69 bar if the primary calibration need is over 400 psi / 28 bar.
4. Achieving repeatability when calibrating a pressure switch
Calibrating a pressure switch can be a time-consuming task and repeatability is key to success. Achieving repeatability requires the user to apply slow changes in pressure to the switch as it approaches its defined set or reset point. Not only do you need to determine where the switch sets, you need to make sure that the Vernier or fine adjustment mechanism of your test pump has the capability of varying pressure up to the set point and back to the switch reset point. Since these adjustments are manual, achieving repeatable measurements of the set/reset points can be difficult. With practice, technicians can gain the experience to get the fine adjustment of the pump within range of the set and reset point pressure with more regularity. This process can be further simplified by selecting a pump with a wide fine adjustment range, allowing you to more accurately make adjustments to meet measurement requirements.
Fluke 729 provides a big productivity boost for pressure calibration.
Systematizing Pressure Calibration
Shields further explained how Fluke has designed the new 729 Automatic Pressure Calibrator to systemize, streamline, and enhance the efficiency of the process, based on customer feedback and the company’s engineering know-how. The 729 has an internal electric pump that provides automatic pressure generation and regulation in a portable package. The 729 allows users to type in a target pressure, and the calibrator will automatically pump to the desired set-point. Then, internal fine adjustment control automatically stabilizes the pressure at the requested value. The Fluke 729 can also automatically test multiple pressure test points and document the results. The processor in the 729 makes it an automatic test instrument based on the defined procedure. Built-in HART communication capabilities enable HART transmitter mA adjustments, light HART configuration and the ability to adjust to applied 0 % and 100 % values. Calibration Management Software helps to manage instrumentation records, create scheduled tests, generate reports, and manage calibration data.
A Tool to Enhance Process Productivity?
The integration and simplification of the process using an instrument such as the Fluke 729 Automatic Pressure Calibrator provides the kind of tool that increases productivity and is a prime example of the type of technology which younger professionals can expect to work with in the processes of the future.
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