Using NI Data Acquisition Devices and LabVIEW to Test Thousands of Hydraulic Components

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"We used LabVIEW as our development platform because of the hardware/software integration with LabVIEW and NI data acquisition devices."

- R. Klein Wolterink, Klein Wolterink Automation

The Challenge:
Developing a test bench to test more than 3,000 types of hydraulic aerospace components, such as rotating and nonrotating parts, in accordance with the Component Maintenance Manual instructions.

The Solution:
Using NI data acquisition (DAQ) devices with LabVIEW software to develop a flexible system so the user can configure tests at run time, collect data, control the system, generate reports, and reduce equipment cost by implementing the same setup for testing many different components.

R. Klein Wolterink - Klein Wolterink Automation

Hydraulic Test Bench for Aerospace Components

Every hydraulic aircraft component must be tested regularly for safety. Suppliers require airline operators to carry out tests on these devices according a strict protocol called the Component Maintenance Manual (CMM). The protocol prescribes which sequential steps and tests have to be carried out, at which pressures, and which pass/fail criteria apply to each test.

Most hydraulic test stands today are dedicated to test one or a limited set of hydraulic devices. These rigid test stands can cost up to 60.000 Euros and contain a fixed regulator, which reduces usability to only a limited set of tests.

Hycom designs and manufactures advanced hydraulic systems, and decided to develop a more flexible test stand that can test a variety of hydraulic parts such as pumps, valves, cylinders, and servos. Our new system can run in semiautomatic mode in which the operator initiates different test steps prescribed by the CMM, or fully automatic mode in which NI TestStand controls the LabVIEW application and runs the full CMM test. The system contains a cabinet with flow regulators, pressure regulators, manifolds, and connections to the unit under test (UUT), as well as a touch panel running a LabVIEW application. We define the tests once and save the results. The test operator can load the CMM test with all parameters correctly set and directly carry out and report the test.

Thousands of Configurations Require a Flexible Application

Because it is difficult to deliver an off-the-shelf system that can test many different parts, we developed a test bench that could adapt according to customer specifications and regulatory requirements. Therefore, the user would need to build and configure tests differently depending on the type of part under test. As a result, the software application requires a real-time view of the data in charts and indicators, Y-T and X-Y graphing capabilities with user definable channels to plot against each other, set point configuration at dynamic selection of the feedback signals for control loops, data storage to Microsoft Word format and ASCII, a user interface that can be modified and stored by the user at run time by adding indicators/controls and matching them with inputs and outputs, automated tests, and calibration capabilities.

We used LabVIEW as our development platform because of the hardware/software integration with LabVIEW and NI data acquisition devices. We defined the software requirements and KW-Automation developed the actual software.

Because we have many products and configurations to test, we developed a very flexible application. During installation, the user defines a list of names and connects to the actual data acquisition hardware and the sensors/actuators in the test bench. The test bench also contains some I/O points so the user can connect sensors that are part of the product to test, such as current outputs for actuators.

All I/O points are continuously sampled at either 50 kHz (LVDTs) or 5 kHz, and synchronized using the Real-Time System Integration (RTSI) bus on the PXI chassis backplane. The data is stored in a real-time database and continuously updated in the background. For graphing and capturing short events, the data is available to the user at high sample rates.

We implemented 13 hardware-timed proportional integral derivative (PID) controllers in the software that run at 5 ms intervals. The PID controllers primarily control pressure or flow of devices inside the test bench. We configured the I/O of the PID controllers once during commissioning and stored it in the tag list. In addition to the fixed PID controllers, we have completely user-definable PID controllers so the user can define the PID control function, the output and feedback signals, and the type of controller for each part under test.

To indicate how a part under test should be tested and connected, the user can configure and save the user interface for each particular test including adding controls, indicators, and pictures, and storing parameters and properties for the I/O (tags) and PID controllers.

We have a fixed set of objects on the user interface next to the viewable region of the screen so we can add it to the user interface when needed. The user can drag and drop the objects to the required position. The objects on the screen include numeric indicators, gauges, controls, graphs, Booleans, and picture controls in which the user can load an image of the item under test and the custom PID controller used to connect to the parts. The operators can save the user interface, including the position of the items, and reload it when needed.

In addition to the position of the object, the user can define several properties such as caption, size, engineering units, range, and the connection to the channel or tag name. The user can implement the custom PID controller as a subpanel, a feature that we can use to embed a VI front panel on another VI.

We also implemented a parameters feature. Because operators control the tests through a touch screen, changing parameters can be difficult. Now the user can click on a control that changes the color to blue or red. On the test bench control desk, there are two large red and blue knobs. Turning the corresponding knob will increase/decrease the corresponding control on the user interface. Color is also used to indicate if a line is active or not.

When a test is defined, NI TestStand can automatically call it through sequence files for fully automatic part testing, or the operator can call the semiautomatic test from the LabVIEW application to perform the test.


We have supplied several systems to our users. In many applications we use a PXI system as the core for data acquisition because the cabling is more powerful, the system is  rugged, synchronization is already available in the backplane, and maintenance is easier. Our system uses multiple types of data acquisition boards depending on the user’s needs. Most of the systems contain a counter/timer board for encoders and flow control, an analog output board for waveform generation and driving currents to control actuators, digital I/O boards, analog input boards for measuring flow and pressure, and simultaneous sampling analog input boards for connecting linear-voltage differential transformers (LVDTs). The LVDTs are sampled at a high frequency and software-demodulated to derive position. A typical system can contain as much as 10 data acquisition devices and hundreds of I/O channels that acquire or generate data at 5 kHz intervals.


Our new, reliable system has been installed for several customers and significantly reduces costs. The application architecture allows users to implement the test bench for systems with more than 10 data acquisition devices, creating room for custom systems and adaptations. Furthermore, acquiring, processing, and controlling all the I/O requires a lot of computational power. The LabVIEW application independently balanced tasks and threads and gave us the ability to upgrade the computer from a dual-core to a quad-core processor and experience great performance improvements without having to change any of our code.

Contact Information

Klein Wolterink Automation

Smidsstraat 22

7021 AC Zelhem

Phone: +31 314 620396

Fax: +31 314 620761


Web site:


Hycom BV

Dick de Winkel

P.O. Box 1079

7301 BH Apeldoorn

The Netherlands


Web site:

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