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Posts From January, 2016

Should I Specify an AC- or DC-operated LVDT Linear Position Sensor For My Application? 

08 January 2016 06:02:00 Categories: Comment

Mike Marciante
TE Connectivity (Macro Sensors LVDTs)

An AC-operated LVDT Linear Position Sensor does not contain any internal electronics and requires an external oscillator, carrier amplifier, or demodulators and filters to operate. A DC-operated LVDT Linear Position Sensor is comprised of an AC-operated LVDT and a carrier generator/signal conditioning module.  It maintains all the desirable characteristics of the AC-LVDT, but has the simplicity of DC operation.   

Applications often dictate the choice of an AC- or DC-operated LVDT.  Here are some examples:


  • Extreme temperatures: below -20°C or above 85°C:- Constructed with appropriate materials, AC-operated LVDTs can operate in temperatures from ‑200°C to 500°C.  A DC-operated LVDT, on the other hand, is limited by the properties of the materials in the electronic signal conditioning module. 
  • Hard-to-Reach installations:- While LVDTs with internal electronics may have a 20 year expected life, free-core, non-contact AC LVDTs have an even longer life expectancy.   Their high reliability makes them ideal for installations in locations without easy access.  Without the need for internal electronic components, AC-LVDTs also can be offered in smaller package sizes to fit in compact locations. Remote electronics can be installed in an accessible location away from the LVDT.  
  • High Shock/Vibration Environments:- Sensitive electronic components can be affected by shock and vibration.  Installing an AC- LVDT allows the user to segregate the sensing element from the electronic circuitry. Connected by long cables up to 31 meters (100 feet), AC-operated LVDTs can work in hostile environments with remotely-located electronics that operate in benign areas.


  • Easy and Fast Installation:- DC input/DC output and factory-calibrated output allow for a simple and quick set-up. Using ASIC and microprocessors, internal electronics can provide for more complex processing functions as well as signal conditioning within the sensor housing. As there is need for calibration or reliance on amplification equipment, setup time is reduced as well as overall system cost.
  • Eliminates Signal Conditioning Requirements:- The DC-operated LVDT can eliminate the volume, weight and cost of conventional external AC excitation, demodulation and amplification equipment (ideal for outdoor applications where a control panel may not exist).   They also can produce digital outputs directly compatible with computer–based systems and standardized digital buses, which is desirable in metrology and subsea applications.
  • Loop-Powered Designs:- Unlike voltage signals, current signals will not diminish over a long run of cable.  This makes loop-powered 4-20 mA LVDTs ideal for applications where long cable runs in excess of 1,000 feet are required.  This is a very useful feature in subsea and outdoor applications where control panels can be located far from the sensor.

Benefits of AC- vs. DC-Operated LVDTs at a Glance

AC-Operated LVDTs

DC-Operated LVDTs

Unlimited electrical/mechanical life

Pre-calibrated analog or digital output

Greater shock and vibration resistance

Eliminate reliance on signal conditioning

Wide operating temperature ranges

Integrated error compensation

Smaller package size/hard to reach places

Lower overall system cost

Infinite resolution

Faster set-up time


1. A position sensor was required on the door to a large furnace where temperatures reach 175°C.  Because of its 200°C temperature rating, TE Connectivity’s Macro Sensors HSTAR AC-operated LVDT and LVC-4000 signal conditioner were specified.  While the LVDT was exposed to the high temperatures, the LVC-4000 was mounted remotely where the temperature was controlled to produce a 4-20 mA output.      

2. The Macro Sensors GHSIR Spring-Loaded 4-20 mA Loop-Powered LVDT was specified to monitor structural components on a bridge.  Because control panels on bridges can be far apart, the cable runs between an LVDT and its associated electronics could be as high as 1,000 ft.  Using TE Connectivity’s Macro Sensors GHSIR allowed the customer to make the measurements with little concern over the LVDT’s proximity to the closest control panel.

Lock the backdoor - Connected medical devices creating cybersecurity risks 

04 January 2016 05:06:00
Security experts billed 2015 as the ‘year of the healthcare hack’, with increasing numbers of medical systems attacked by cyber criminals targeting valuable personal data. While cybersecurity is commonly associated with software attacks, the healthcare sector is finding that the hardware it’s employing to improve patient care is creating backdoors. Neil Oliver, technical marketing manager of Accutronics, takes a look at the vital role hardware encoding plays in the battle to secure medical devices
Across the medical sector the amount of digitally stored data is growing year-on-year, and while pharmaceutical companies, healthcare facilities and original equipment manufacturers (OEMs) have to constantly work at keeping hackers out, a hacker only has to be successful once to cause serious damage. For instance, at the end of 2014, the number two US health insurer, Anthem Inc, disclosed a massive breach of its database containing nearly 80 million records.
Medical equipment has taken an evolutionary leap in recent years to take advantage of the developments of the digital age. With the rise of the Internet of Things (IoT), medical devices are ‘connected’, and not just to the Internet. They are often connected right into a healthcare provider’s network, establishing a pathway to data that seems otherwise protected. 
At 2015’s hacker conference DerbyCon, it was revealed that there had been 68,000 attempts at hacking critical medical devices, such as MRI scanners, over a six-month period. Fortunately, in this instance these were fake devices, “honeypots” set up to lure in malicious hackers. This goes to show the importance of addressing cyber security flaws, particularly in devices that leave patients at risk of harm if compromised. 
In the fight to close the backdoor, every measure must be taken to secure the hardware itself. A lack of hardware-based encryption is causing widespread concern about medical equipment and about the reliability of batteries used in such equipment.
Battery counterfeiting is a problem faced by the medical industry on a scale never before witnessed in the sector. The ready availability of grey market, untested copycat batteries, possibly using inferior components, means that many life-critical devices used in our hospitals and medical establishments may be unreliable or unsafe to use.
Accutronics has worked hard to tackle this problem, developing a new CMX series of smart batteries and chargers. The new range incorporates some innovative features, including SHA-1 hardware encryption.
SHA-1, which stands for secure hash algorithm, is a cryptographic hash function designed by the United States National Security Agency (NSA). The algorithm is flashed onto the smart battery's fuel gauge before being sealed in during production. At the same time, a software update is made on the host medical device. Upon insertion, the battery is challenged to complete a calculation within 100ms, if it matches with the one performed by the host device, it's genuine, otherwise it's fake and can be rejected for non life-critical applications. 
It’s time to lock the gate behind us and shut cyber criminals out of medical devices by building cybersecurity and encryption into the equipment. Doing this means thinking of every part of the machine, even something as seemingly insignificant as the battery. Building encryption into the hardware itself will provide the first line of defence against those who would use medical devices to cause trouble, reducing the threat to life and reducing the potentially massive costs of leaving the backdoor unguarded. 

Michelle WinnyMichelle Winny

With a combination of news, products and feature articles, Michelle provides up-to-wire commentary on new technology and legislation. Coupled with in depth coverage for specifiers and purchasers of electronic components and equipment, Michelle brings everything within the electronics market directly to her readers.