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Hydraulic Valve Test Bench Setup Utilizes an ADwin DAQ System

CAS DataLoggers Helps Design, Manufacture and Program Test Setup

In 2009 CAS DataLoggers helped design, assemble and program the data acquisition and control solution for an Ohio manufacturer who needed a test bench setup for their directional control valves. In this application, hydraulic fluid flowing through a line inside a model of military aircraft was causing destructive pressure spikes when a remotely actuated hydraulic valve rapidly opened and closed, loosening the fittings in the hydraulic lines. Pressure spikes, similar to water hammers, are caused when the flow rate of moving fluid is suddenly changed. This generated pressures measuring into the thousands of PSI’s, producing substantial force and causing a major inconvenience for flight crews which had to spend hours retightening the fittings caused by these leaks. In response, the customer developed a new valve specification which stated that the actuating period had to be slower than a certain value to limit this. The specs also included a certain value of shock factor based on the shape of the pressure spike which also had to be below the given value listed in the specs or the part would be rejected. After developing a new valve design, the manufacturer required a highly accurate test system to prove the new parts were up to spec. That’s when they contacted CAS DataLoggers to work with them to develop a unique test stand for this application. This multi-point test setup would require a highly accurate test data acquisition and control system that could operate in real time, making calculations as each measurement was processed.

System Design:

CAS DataLoggers Managing Engineer Terry Nagy worked with the manufacturer to develop a directional control valve shock factor test system. This semi-automated test stand is centered around the ADwin-Light-16 Real-Time Data Acquisition and Control System as part of a touchscreen industrial computer. The touchscreen display is mounted on the front of the enclosure and features an on-screen keyboard for data entry. An Ethernet port allows the PC to connect to the in-house network for data storage, transfer and printing.

The computerized system is housed in a NEMA 4 enclosure which houses the PC, data acquisition system, pressure sensor signal conditioners, opto-isolator modules and the power supply. Power to the main enclosure is 120 VAC, single phase, 60 Hz.

The ADwin system used here is an intelligent real-time data acquisition system performing electrical measurement, featuring 8 16-Bit analog inputs, 2 16-bit analog outputs and 6 TTL/CMOS compatible digital inputs and outputs. The system also utilizes a local 32-Bit SHARC DSP with its own local memory to handle system management, data acquisition, on-line processing and control of outputs. Several system configurations are available including PCI, CompactPCI, and EURO USB configurations, or external USB or Ethernet.

The manufacturer’s pressure transducers were hooked up through connectors compatible with the existing connectors on the pressure sensors to facilitate easy exchange of sensors. Additionally, 4 signal conditioning modules were supplied with the ADwin to provide excitation and amplification for the 2 mV/V-sensitivity pressure sensors. CAS DataLoggers also provided a pair of opto-isolator modules to interface between the ADwin system and the 28 VDC pilot valves.

Test Operation:

ADwin Data Acquisition ProcessThe test was designed for small production runs of 20-50 parts. First an operator connected the unit under test to the test station and started the test execution software on the PC using an industrial 15” color touch screen LCD display panel (rated IP-65) and on-screen keyboard. Users then entered the valve’s serial #, the appropriate sequence (detent or non-detent) and the correlation factors for each percentage for proper calibration during test operation. Test Information included user name, date, part #, part serial #; Cycle Timing; and ADwin Settings. During the test users could also view test and plot settings.

The test program stepped through the test sequence using the appropriate limits, actuated the relays for the supply valve, automatically collected pressure information, and calculated the surge peak pressure and shock factor and pass/fail information as required.

The interface gave users an overview of the test data from the transducers during test execution; each test lasted for 10 cycles, ie a 10-second period of time. During operation, the display graphed the data from the last cycle portion, its maximum valve pressure, and the maximum shock factor calculation for the cycle portion’s data set. Meanwhile a status bar displayed the cycle, portion of the data being displayed, and the valve settings for that data set.

In the Transducer Readings frame, a real-time display of each transducer was given.  This was used to verify the correlation factors for each transducer. In the Solenoid Control frame, colored circles indicated the state of each solenoid valve. Green indicated that the valve is open and red indicated that the valve is closed.  The Solenoid On/Off button acted as a toggle for manually changing the state of each solenoid valve.

The ADwin-Light-16 system enabled real-time development with the included ADbasic software, which defined the processing sequences executed on the hardware and enabled programming of mathematical operations and functions which were executed immediately after each sampling step. Using ADbasic, engineers optimized and compiled the program code with a mouse-click. After being loaded on the system by ADbasic or a graphical PC user interface, the real-time processes executed independently. ADbasic contained the functions to access all inputs and outputs as well as functions for floating-point operations, process control and communication with a PC. A library was provided which contained standard functions such as filtering, various examples for counter use, closed-loop controllers, function generators, etc. which lead to a faster program implementation.

The ADwin generated graphs which plotted the data on 2 axes: Pressure (p) and Time (t). The graphs showed a point-by-point derivative used to calculate the slope of the data. Users also needed to determine the time delta, and the ADwin excelled at calculating this point by point, with each step timed at high accuracy. The ADwin real time DAQ system also calculates the peak pressure and shock factor. The shock value is calculated by a quick formula:  Differential Pressure (DP) / Delta Time (DT).

Test Documentation:

The results of each test were stored in a data file and were also available as a final report that could be printed when the test is complete, giving all of the test results. Likewise, specific part information was stored in a file segmented into 3 parts: Part Numbers, Part Timing, and Part Limits. The Part Timing section defined the cycle portion timing for the part number. The Part Limits defined the maximum surge factors for each transducer for the part number.

Benefits and Value-Added Support:

The test stand CAS DataLoggers helped the vendor develop for this unique application performed exactly as it was intended. CAS DataLoggers provided all the measurement instrumentation for this application and helped design, manufacture, assemble, program, debug and test run the system. CAS DataLoggers Engineer Terry Nagy provided free technical support, onsite training, and also developed the PC-side user interface. Telephone technical support is available for the life of the system at no charge. The assembled system was successfully demonstrated at the customer’s site, consisting of execution of a full test plan on a known good valve and simulation of 2 failure modes.

ADwin was the ideal solution here as it contained its own real-time operating system so it could run independently of a PC. This way it could maintain the high accuracy this test bench application needed to ensure the vendor always delivered an up-to-spec part. Processing of each measurement occurred immediately after acquisition thanks to the ADwin’s onboard SHARC DSP. This way the manufacturer is able to more easily meet their spec and prove it to their customer with the ADwin’s file info containing all the measurement algorithms and calculations. If the vendor had tried to use a DAQ system based on MS Windows, users wouldn’t be able to maintain that timing very accurately because Windows processors have to multitask while attempting to keep pace with calculations, i.e. they don’t run independently of the PC as ADwin does.