The World’s Most Advanced Linear Variable Differential Transformer Signal Conditioner

John Matlack, Executive Sales and Marketing Director for the Alliance Sensors Group talks to AZoSensors about the world’s most advanced linear variable differential transformer signal conditioner.

Can you discuss exactly how the S1A model signal conditioner works?

The model S1A is a signal conditioner for an LVDT, so to understand how the S1A works requires understanding what an LVDT is.

The acronym LVDT stands for Linear Variable Differential Transformer, a type of position sensor.  As a transformer, an LVDT has a primary and two identical secondaries that are connected differentially.

It operates from an AC voltage and frequency much different from that of the power line and uses a movable core to vary the amount of primary voltage being coupled into each secondary. This movability of the core permits an AC-LVDT to be used as a linear position sensor in typically hostile environments.

But is absolutely necessary for any LVDT to be used with signal conditioning electronics like the S1A that can supply the needed low voltage AC at the proper frequency to operate the LVDT and convert that sensor’s output signal into a suitable analog output, either high level DC voltage or current.

What are the main features of this unit? 

Prior to the advent of the S1A, setting up an LVDT signal conditioner required the user to know certain parameters of the LVDT, make some calculations to set DIP switches or movable jumpers within the module, and then calibrate the signal conditioner to the LVDT sensor by moving the workpiece whose position was being measured between its range of motion while adjusting two or more trimpots. This calibration process was very tedious and usually took 20 to 30 minutes per sensor.

The main features of the S1A are:

1. The S1A supplies the necessary voltages to operate the LVDT, uses a microprocessor DSP to do all sensor I/O calculations required without any user input, and uses a pair of front panel pushbuttons to set the full scale and zero calibration points locally, all this calibration being finished in about two minutes.
2. The S1A is the first LVDT signal conditioner to offer an RS-485 half-duplex multi-drop communications bus that permits the module to be remotely calibrated and analog output data to be logged by using a GUI offered for free by ASG. This same RS-485 bus also allows a user to save calibration settings for future hot swapping of modules.
3. The S1A has substantial sensor failure diagnostics that can be used to find both set-up problems and/or operational failures and to set off an alarm or annunciator or to send an alarm signal to a DCS.  Also, in the event of a sensor failure, the analog output is driven out of range, which, with the right algorithms, permits the DCS to know that an error has occurred and to disregard the feedback input from that sensor. (This is particularly important to users of redundant sensors, such as in process and power plants, to prevent signals of an in-range output value from a failed sensor being averaged with correct outputs.)
4. Ordinary LVDT signal conditioners, when used in multiples, require master/slave syncing at the same excitation frequency so that there is no chance of beat frequency effects from individual units operating at slightly different frequencies.  However, if the master for these systems fails, the slaves free run at their own individual frequencies, so the undesired beat frequency effects will occur.
5. The S1A has a unique auto-mastering system that generates a new master in the unlikely event of a failure of the original master, assuring that all the slave modules are still running at the same excitation frequency. The S1A is the first LVDT signal conditioner to offer color-coded plug-in terminal connectors to make the necessary connections to the LVDT and the rest of the measuring system. This makes the installation very simple, especially in multiple module systems, and facilitates any hot-swapping in the future.
6. Every S1A is burned in for a minimum of 48 hours, using a start-stop cycle mode, so they are offered with a 2-year warranty instead of the industry-standard 1 year warranty.

Exactly how has the S1A design raised the bar for manufacturers in the same market area?

Until now, the S1A has been the only LVDT signal conditioner offered with all the features noted above.

How does the GUI system allow for calibration of this new model?

An S1A LVDT signal conditioner has an RS-485 half-duplex multi-drop communications bus with up to 16 modules. The GUI offered for free by ASG has screens that emulate the actions of a local user operating the front-panel push-buttons, which permits any particular module to be remotely calibrated.

The GUI also allows the analog output data from each module to be logged and each module's calibration settings can be saved in a file to be used for hot swapping. Using a PC with a wireless RS-485 converter, the GUI can control the set-up and operation of all the S1As from virtually any location.

Is this model used with any other systems?

An S1A works with 3-wire, 4-wire, 5-wire, and 6-wire LVDTs and RVDTs, along with inductive half-bridges and LVRTs found in power plants. The range of systems in which it is used includes industrial automation systems, QA inspection systems, data acquisition (DAQ) systems, and all kinds of PLC- and PC- based industrial and process control systems.

How would you compare this S1A model to similar products?

It is by far the best LVDT signal conditioner currently in the marketplace, offering outstanding value for its very competitive price and a 2-year warranty.

What would you consider as the future developments of this technology?

If there is sufficient market demand, sensor output linearization is a feature that could be offered.

What are the main areas of applications for the S1A?

Power generation plants, chemical process plants, waste water treatment facilities, pulp and paper mills.

The S1A can also be set up remotely. What does this process involve and for what applications?

Usually the user hooks up the S1A's RS-485 2-wire bus to a serial or USB port converter attached to a PC and uses a terminal program like Hyper Terminal or the ASG GUI program to communicate with the module. Instructions are available for using the GUI and are available in the manual for using a terminal program.

Are there any new products in the pipeline for Alliance Sensors Group?

We are a company that strives to be the best in our industry on many different fronts. Our competitors are typically behind us in technological innovation.

We recently introduced a truly remarkable linear position technology that is a direct replacement in the fluid power in-cylinder market for the incumbent magnetostrictive sensors currently being used. This technology is superior when considering shock, vibration and high temperature operation.  

Along with these advantages, it has a less complicated mechanical structure with fewer parts, substantially reducing possible failure modes, and typically the installed cost is lower. We anticipate making refinements to existing products like the S1A, our linear position sensor.  

About John R. Matlack

John Matlack began his career in the sensor industry by working with Lucas Schaevitz in 1990. Initially hired as an applications engineering, he was later promoted to business development manager for the position product line and then regional sales manager for numerous sensor technologies under the Measurement Specialties portfolio. In 2009 John left MSI to and worked for Macro Sensors as Global Business Development Manager.

John joined Howard and Harold Schaevitz after Alliance Sensors Group was formed to head the Sales and Marketing Department.