Customer Solutions
Universal DC Motor Controller Test Station
Author(s):
Heath Buchanan, Kearfott Guidance & Navigation Corporation
Industry:
Government/Defense
Product:
LabVIEW, NI TestStand, PXI/CompactPCI
The Challenge:
Automating the testing of a wide range of new and existing DC motor controller circuit assemblies.
The Solution:
Developing a test station using PXI products, LabVIEW, and TestStand.
Introduction
Kearfott Guidance & Navigation Corp. designs, develops, manufactures, and supports land, air, sea, and space navigation and guidance products for military and commercial customers worldwide. Kearfott’s operations occupy more than 1 million square feet in design and manufacturing facilities where its personnel have produced more than 100,000 inertial devices and over 4 million precision components. The Black Mountain, North Carolina, facility focuses on inertial measurement unit sub-assemblies, linear variable differential transformers (LVDTs), resolvers, and electric motors. Kearfott also designs and manufactures many different DC motor controller circuit assemblies. These circuit assemblies control fin actuators on a wide range of guidance applications and primarily control three phase brushless DC motors, which operate in a closed-loop, position feedback system for fin attitude. Potentiometers provide position feedback information. The controllers use this and the command voltage to determine the error signal for motor control.
Test Requirements
The test station supplies power and stimulus to the controller. Measurements are then made of certain key parameters. Command and position feedback voltages are supplied to the controller under test. Hall effect device inputs are then simulated, and the controllers are checked for proper motor output sequencing for different command and position feedback voltages. Power is supplied to the unit and onboard voltages are measured. The motor outputs are loaded to certain current levels, and we measure the output FET voltage drops. The motor outputs use pulse width modulated (PWM) DC voltage to control the motors. We can measure the duty cycle of this PWM control. The controllers use frequency compensation circuitry to tailor the frequency response of the system. The test station can examine the step response of the controller.
The Test Station
We designed the station to automate testing on many different DC motor controllers. The tests required quick implementation for new or existing products on a common test platform. We selected National Instruments products for their availability, reliability, and ease of software development and integration. PXI was specified because of its ruggedness over conventional PCs and its cost advantage over VXI test systems.
A PXI-8156 embedded computer, using the Windows NT 4.0 operating system for security, controls the test station. This computer features an Ethernet connection for remote access of test data.
Measurements are made via two PXI modules. The PXI-6031E is a multifunction module, which features 64 channels of analog inputs. These channels measure many different voltages of less than 10 V. The 8 TTL digital input/output lines simulate hall-input signals to the controller and enable the controller. The two analog outputs provide command and position feedback voltages.
The NI-5102 15 MHz digital oscilloscope, operating in conjunction with a NI 2503 relay switch PXI module, makes measurements of greater than 10 V. The NI 2503 is configured in 1-wire multiplexer mode, with 48 inputs. The multiplexer accesses many different points with the scope, and high current switching of the motor outputs is accomplished by using two ASCOR 7010 PXI modules, which feature eight 10 amp relays each.
Two GPIB controlled power supplies supply power. A Hewlett Packard E3631A power supply provides +6, +25, and -25 VDC. While a Sorensen DHP80-25 provides motor voltage of up to 80 VDC and 25 Amps. The controllers are electrically loaded using an Hewlett Packard 6050A programmable DC electronic load, which provides versatile loading without the use of many different set-value resistive loads.
MAC Panels L2000 Series test interface products connect the instruments to the controllers under test. All connections to the instruments in the test station are terminated to the receiver. The interface test adapter (ITA) contains signal buffering and the interface cable to the controller under test.
All of the instruments are mounted in an Equipto workstation. This workstation features a desk like work area for the monitor, keyboard, mouse, and the controller under test. The workstation has a 19-in. bay for mounting the instruments.
We programmed the test station’s operation using National Instruments LabVIEW for all measurements and control of instruments. National Instruments TestStand operates as a test executive to control the automation and documentation of the testing process. Test results are stored to the computer’s hard drive and are available anywhere over the corporate network.
Results
By using National Instruments hardware and software, development of our test station was greatly simplified. TestStand is an excellent tool for bringing together many different LabVIEW VIs for measurement and automation of the test station. PXI provides a compact and rugged environment for the embedded computer and the measurement and control modules. The easy-to-use VIs of each PXI module provide straightforward integration of our hardware and software. With all of these attributes, you can focus on your primary purpose, to develop a comprehensive test in as short a period of time as possible.
For more information, contact:
Kearfott Guidance & Navigation Corporation,
Web: www.kearfott.com
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