LINEAR MOTION FEATURE
EN60068-2-1 and EN60068-2-2. European Standards (EN) are being ratified by one of the three European Standards Organizations, CEN, CENELEC or ETSI. To pass the test for low temperature operation, a device must operate at rated load for 96 hours while thermal soaked at -40˚C. Likewise, to pass the test for high temperature operation, a device must operate at rated load for 96 hours while thermal soaked at +85˚C. Actuators must also be able to pass such tests after immediate and dramatic temperature variations. An example would be an actuator mounted to construction equipment used in cold climates that is then pressure washed with high temperature water at the end of the day. The incorporation of onboard
electronics, in addition to requiring environmental protection, also contributes to protection from extreme temperatures. Where protection from overheating traditionally has been provided with a thermal breaker inside the motor, today it is embedded in the circuit board. The thermal protection on the circuit board protects both the motor and the circuit board from overheating and allows the actuator to complete the stroke before shutting down. The traditional breaker on the motor will stop the actuator anywhere in the stroke if overheating occurs. The electronics also include thermal compensation at low temperature, allowing the actuator to draw the higher current required at low temperatures without nuisance tripping.
SHOCK AND VIBRATION
The latest shock testing profiles cover housings, structural bolts and any printed circuit assemblies/sensors included in the product. Guided by the EN60068-2-27 test standard, the test for operational shock involves 100 operations of 400m/s², 6ms duration shock pulses, which should be repeated in each of three mutually perpendicular axes. The larger components on the printed circuit board have RTV applied to secure them to the board; and typically fail without the added support in high vibration or shock situations. EN60068-2-32 defines testing for
drop shock. It details dropping a device onto a steel or concrete floor from a 1000mm platform in both directions of each axis, and repeating that for a minimum of six drops. Off-highway equipment often has to perform effectively amidst constant vibration. Test protocols, usually OEM-specific, are run to ensure that the actuators will be able to withstand challenging vibration profiles. Testing is conducted with the unit not powered or
Fluid (DEF) are DIN 70070-05, AUS 32, ISO 22241-1.
VOLTAGE VARIATION Voltage variation can result from weak batteries, faulty voltage regulators, long wiring runs, corroded wiring connections, and poor grounding. The latest electric linear actuators, like the Thomson Electrak HD, are tested vigorously to withstand voltage levels for which they are designed as well as for voltage spikes, reverses in polarity and short circuits. Testing to ensure that an actuator
operating and mounted on vibration equipment guided by power spectral density levels. The actuator being tested should extend half of the stroke length and be tested in three orthogonal axes for 24 hours each. These multiple points of support
allow the actuator to survive in many high vibration applications. The larger components on the printed circuit board are mechanically secured to the board and cushioned for high shock or vibration environments.
PROTECTION FROM CORROSION Salt-water immersion and salt spray can be a major source of corrosion in applications associated with shipping or other at sea operations. ASTM B117-11 is a test standard for salt water, which states that a device should be able to withstand a minimum of 500 hours of salt spray and be operational at the end of the test with no ingress of the salt spray. Other common sources of corrosion include hydrocarbons, urea and fertilizers. One of the most widely applied standards for chemical resistance is ISO 15003, which provides design requirements and guidance for the manufacturers of electrical equipment used in mobile agricultural machinery, forest machinery, landscaping and gardening machinery. It provides test protocols for specific environmental conditions and defines severity levels for extreme environmental conditions that might occur during typical operations. Testing for chemical resistance
requires the ability to withstand three days of operation amidst the following chemical concentrations: • Diesel fuel – 100% • Hydraulic Oil – 100% • Brake Oil – 100% • Ethylene Glycol – 50% aqueous solution • Urea Nitrogen – saturated solution • NPK Fertilizer*9 (7.5% each N, P, K) – saturated solution Other standards applied to corrosion resistance, particularly Diesel Exhaust
The Thomson Electrak HD electric actuator was designed for mobile off-highway vehicle applications
can accept its minimum and maximum operational voltage levels without causing damage involves demonstrating that it can withstand a defined amount of voltage for a specified time period. For example, a 12V DC actuator should be able to operate at between 9V DC and 16V DC for five minutes. An actuator rated for 24V DC should be able to operate at between 18V DC and 32V DC for five minutes. To ensure an actuator can handle accidental operational voltage spikes without
damage, a 12V DC actuator should be tested to handle
spikes to 26V DC for five minutes.
Extension tube wipers and housing gaskets protect the Thomson Electrak HD actuator mechanics and onboard electronics from contaminants and water intrusion
Likewise a 24V DC actuator should be tested to handle 36V DC for five minutes. To ensure that the actuator would
survive polarity reverses, a 12V DC actuator should be able to withstand minus 26V DC operation for five minutes, while a 24V DC actuator should be able to withstand minus 36V DC for five minutes. The ASAE EP455 test standard covers
short circuit testing while ISO 10605 provides ESD testing procedures.
PROTECTION FROM ELECTROMAGNETIC INTERFERENCE Printed circuit boards are subject to electromagnetic interference (EMI) from a wide variety of sources. ISO 13766 and ISO 7637-2 are the most important standards providing testing guidelines for EMI. The following are among the test protocols they offer: • Conducted Emissions - ISO 13766 • Radiated Emissions - ISO 13766 • Electromagnetic Immunity - ISO 13766 • Inductive Load Switching - ISO 7637-2 • Cranking - ISO 7637-2 • Load Dump - ISO 7637-2 • Positive Inductance Transient Test - ISO 7637-2
• Positive and Negative Coupling Test - ISO 7637-2.
Linear Technology
www.thomsonlinear.com
DESIGN SOLUTIONS | APRIL 2016 39
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