CHOOSING THE RIGHT OUTPUT SIGNAL FOR THE APPLICATION
LVDT position sensors are available with various output signals. Learn about some of the variables and options.
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 LVDT output signal.
AC-OPERATED LVDT APPLICATIONS
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.
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 suitable 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 and Vibration
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.
DC-OPERATED LVDT APPLICATIONS
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 no need for calibration or reliance on amplification equipment, setup time is reduced as well as overall system cost.
Helps Eliminate Signal Conditioning Requirements
The DC-operated LVDT can help eliminate the volume, weight and cost of conventional external AC excitation, demodulation and amplification equipment (suite 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 Option
Unlike voltage signals, current signals will not diminish over a long run of cable. This makes loop-powered 4-20 mA LVDTs suitable for applications where long cable runs in excess of 1,000 feet are required. This is a very useful feature in sub-sea and outdoor applications where control panels can be located far from the sensor.
Benefits of AC versus DC LVDT at a Glance
|AC LVDT||DC LVDT|
|Unlimited electrical and mechanical life||Pre-calibrated analog or digital output signal|
|Greater shock and vibration resistance||Helps eliminate reliance on signal conditioning|
|Wide operating temperature range||Integrated error compensation|
|Smaller package size fits in hard to reach places||Lower overall system cost|
|Infinite resolution||Faster set-up time|