USB Data Acquisition Solution for Quantifying Fluid Flow Measurements Using Portable Data Acquisition Enclosure

Author(s):
Bruce L.. Wilcox - Wilcox Design Service

Industry:
Manufacturing

Products:
Data Acquisition

The Challenge:
Developing a new valve test and measurement system that is portable and capable of increasing efficiency.

The Solution:
Using National Instruments USB data acquisition (DAQ) hardware to develop an extremely cost-effective and lightweight solution.

Wilcox Design Service was approached by one of our customers, a large valve manufacturer, to develop a new, portable test and measurement system. The customer also wanted to increase test efficiency with the new system and find a better method for storing the equipment between tests. To improve measurement techniques used in a fluid flow laboratory, we researched portable data acquisition products that would meet these requirements.  

Previously, when a user completed a test, there was a high potential for damage to occur to test equipment using the original set of hardware and instruments. We selected high-performance, bus-powered USB as the new protocol for data transfer.

The customer’s test setup needed to meet ISA-75.02 requirements (formerly ANSI/ISA-S75.02-1996). Using a valve body as a test specimen, we recorded test data for pressure drop versus valve disc position. Based on measurement accuracy and sampling, we could tweak a particular valve device so the design provided the lowest pressure drop possible for a given flow rate.  

A standard flow test for valves requires flow, temperature, and absolute line pressure measurements. The main goal of the test is to establish pressure drop versus flow rate. We selected Rosemount Model 3051 differential cells for the pressure measurement sensors. Based on customer specifications, the end user can select a pressure measurement device. Many types, ranges, and accuracies are available. We chose a 3 in. Foxboro (Invensys) 8300 Series Sanitary Magnetic Flowtube. For temperature measurement, we inserted a Rosemount Model 3144 approximately 10 pipe diameters upstream of the Foxboro flowmeter. Using the four signals mentioned above, we established flow based on the velocity criteria of the valve body (line-size). For data acquisition, we used National Instruments LabVIEW, writing a LabVIEW VI file to acquire sensor data and display measurements during testing. We also wrote a second VI for data analysis.

The NI USB-9215A DAQ module was the products of choice. The module can handle four simultaneous analog input channels at 16-bit resolution.

NI USB-9215A modules provide integrated signal conditioning; therefore, minimum connectivity and set-up issues occurred during design. In this instance, each sensor measurement signal was based on 4-20 mA. We used a Sola power supply that provided 0-10 VDC output. For the sensor connection termination box, we used precision 1/4-watt, 0.1 percent wire-wound resistors. Signals sent to the USB module were accurately converted from 4-20 mA to 0-10 VDC.

In the final design, we chose a portable, lightweight enclosure and customized it to accommodate all measurement devices.

Total sampling time for a standard test during initial test experiments was approximately five minutes. The maximum sampling rate used to acquire all four channels simultaneously was 1,000 samples per second. This yielded 300,000 data points for a five-minute test. We adjusted subsequent tests to sample at a rate of 4,225 samples per minute, or 70 samples per second. Accuracy results based on flow were calculated to be ±0.03 percent, or 0.225 gpm. Accuracy results based on pressure were calculated to be

±0.04 inches water.

Standard individual test times each require approximately 15 minutes of data acquisition time. Typical design evaluations include a total of four 15-minute experiments. Measurements are acquired for position versus flow data on each valve specimen. Butterfly valves evaluated were quarter-turn (0-90 degrees) of valve disc rotation, representing travel from the open to close position. When the valve disc is positioned to each degree of disc rotation, during testing, a settling time of one minute is provided prior to acquiring USB data to allow the fluid flow to stabilize. We acquired all data using NI LabVIEW. 

The portable data acquisition enclosure and associated hardware using high-powered USB technology performed superbly in experiments. We estimate the solution saved approximately 30 minutes per test over the original test system. Test equipment setup time saved using the new product was approximately 12 minutes per experiment. Cost savings associated with testing (using USB) yielded approximately $1,100 per valve evaluation.

Author Information:
For more information on this Case Study, contact:
Bruce Wilcox
Wilcox Design Service
Tel: (401) 762-6577
wds1022@cox.net

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