Glossary of Terms

A

Accuracy

The accuracy of all Solartron Metrology Digital Displacement Sensors, Gauge Probes and Displacement Transducers is quoted as a % of the linear displacement measurement.


D

Direction of Linear Displacement Measurement

The direction of linear displacement for an LVDT transducer is defined as follows:

● Outward movement is linear displacement from the body of the displacement sensor or displacement transducer.
● Inward movement is linear displacement towards the body of the displacement sensor or displacement transducer.

Displacement Sensor Tip Force

The tip force of the linear displacement transducer is defined as the force excreted on the item being measured at the mid-point of the displacement transducer measuring range.
 



H

Hysteresis

Hysteresis of an LVDT Sensor or gauge probe measurement is the difference from the true measurement when the direction of measurement is reversed.


 
L

LVDT (Linear Variable Differential Transformer)

What is an LVDT?

Linear Variable Differential Transformer (LVDT) Displacement Sensors or Gauge Probes are devices that measure linear displacement. This type of displacement transducer has a reputation for long life with reliable measurements providing a cost-effective solution for many measuring applications. LVDT transducers or gauge probes are used wherever fast and accurate linear measurements are required to ensure good process control.

Fundamentals of an LVDT

● LVDT Linearity
Linearity is defined as the deviation of an LVDT displacement transducer or Half Bridge sensor’s output from a straight line.

● Sensitivity
This is the specified magnitude of the output with respect to displacement (mm) and energising voltage (V) for an LVDT sensor or Half Bridge displacement transducer. It is expressed in mV/V/mm.

● LVDT Measuring Range (Calibrated Range)
The measuring range over which the LVDT displacement sensor specification is guaranteed. For LVDT transducers this is normally expressed as a measurement either side of the LVDT displacement sensor Electrical Zero.

Example: an LVDT linear displacement transducer with a measuring range of 2 mm will normally be defined as ± 1 mm

● LVDT Mechanical Range
The total physical movement the displacement transducer moving part can travel.

● LVDT Electrical Zero
Electrical zero is defined as the position of the moving part when the electrical output of the LVDT linear displacement sensor is zero. (Note: Sometimes known as 'Null').

● LVDT Inward Movement from Zero
This is the total mechanical movement inward from the electrical zero of an LVDT sensor or Half Bridge sensor. (see also Pre-Travel).

● LVDT Outward Movement from Zero
This is the total mechanical movement outward from the electrical zero of an LVDT transducer or HB transducer. (see also
Post-Travel).

● Pre-Travel
The mechanical movement from the LVDT transducer fully outward position, (where the moving element is against a mechanical limit stop) to the start of the LVDT measuring range.

● Post-Travel
The mechanical movement from the end of the LVDT measuring range (inwards) to the fully inward position, where the moving element is against a mechanical limit stop.

● LVDT Energising Voltage
The voltage used to energise the LVDT displacement sensor or Half Bridge sensor. It is specified as a sine wave in V rms at a specific Energising Frequency.  The energising voltage is the range over which the LVDT transducer will operate, the LVDT transducer specification is guaranteed only at the calibration energising voltage.

● LVDT Energising Current
The current required to energise the LVDT Displacement transducer. It is dependent on the energising voltage and is expressed as mA/V. It also varies with the energising frequency.

● LVDT Energising Frequency
The allowable range of frequencies used to energise an LVDT or Half-bridge transducer, it is specified in kHz. The energising frequency is the range over which the LVDT transducer will operate, the LVDT transducer specification is guaranteed only at the calibration energising frequency.

● LVDT Residual Voltage at Zero
The minimum voltage attained for the LVDT transducer electrical zero position. (i.e. the smallest output that can be detected).



O

Orbit® Digital Measurement Network

What is Orbit®

The Orbit® Digital Measurement Network is a system for integrating Solartron Metrology’s digital displacement sensors (like LVDT) easily and quickly to create linear displacement measuring solutions. Digital displacement sensors (which are enhanced LVDT type sensors) can easily be integrated with PCs or PLCs and data can be collected at up to 4000 measurements per second.

Orbit® Controller

Hardware that controls a network of modules and is used for communicating with the Orbit® modules such as the Digital Displacement Sensors. The controller provides the link between the Orbit® network and a PC or PLC.

Orbit® Module

A module or digital displacement sensor (gauge probe) that can be connected to the Orbit® System as part of a Network Channel. Modules and linear displacement transducers perform various precision measurements and interface to the external world.

Orbit® PIE

An electronics module connected to a digital displacement sensor which allows the displacement transducer or gauge probe to be easily connected to the Orbit Network

T-CON

A three way connector containing an EEPROM to provide the address of a displacement sensor or module in the Orbit® Network.


P

PIE
Probe Interface Electronics.

 
R

Repeatability

Measurement to re-measurement test repeatability is the closeness of the agreement between the results of successive measurements of the same measure carried out under the same conditions of measurement.

A measurement may be said to be repeatable when this variation is smaller than a pre-determined acceptance criterion.

Solartron uses a method of establishing repeatability where a defined side load is applied to the LVDT linear displacement transducer or gauge probe under test which reflects how LVDT displacement sensors are used in most real applications. Methods of measuring repeatability without applying side load usually give a better result but this may not be reflected in real life applications.