Tip: How to Ensure the Best Resolution in Analog Interfacing

A large portion of our customers' nanopositioning applications utilize analog interfacing for position-command.  As we have discussed before, analog interfacing offers many compelling benefits including high speed, easy synchronizing, compatibility with our patented HyperBit DAC-resolution enhancement, straightforward generation of complex waveforms, and ready compatibility with external-sensor and tracking schemes.

But occasionally we will encounter a customer application where the analog-interfaced nanopositioning system isn't providing the resolution the customer expects.  Most often, this is due to a simple issue: a mismatch between the voltage range of the customer's digital-to-analog converter (DAC) and the voltage range of the position-command input on the nanopositioner.

Consider the case where a 16-bit DAC (such as is common on multifunction cards installed in the customer's computer) offers a -10 to +10V range, but the input to the nanopositioner has a 0 to 10V range.  The card's "16-bit"ness means that its 20V range is spread over 216 steps... that's 65,536 steps.  So the voltage resolution is 20 ÷ 65536 = 0.3mV.  If the card were set to provide a range of 0 to 10V, then its resolution would be 10 ÷ 65536 = 0.15mV ...in other words, the resolution would be improved by a factor of two.  The mismatch means an entire bit of resolution is lost!

Many (but unfortunately not all) multifunction analog I/O cards offer a configuration option (accessible, for example, via National Instruments' Measurement and Automation Explorer utility, NI-MAX, or via NI-DAQmx subVIs in LabVIEW) for setting the analog range of the DAC.  Certainly, any application benefits from matching the analog ranges as closely as possible.  For those occasions when it is not supported by the hardware, consider HyperBit as a way of recovering that lost bit... and many more.

Read these papers for the latest on high-througput digital interfacing.

Introducing Digital Control at an Analog Controller Price

E-709 Digital Piezo Motion  Controller for Nanopositioning
High Resolution Digital Servo Piezo Controller at Analog Price

PI's groundbreaking E-709 Compact and Cost-Optimized Digital Piezo Controller leverages the very latest in digital electronics technology for dramatic value and performance.  The unit features a very compact, panel-mount package and includes USB and analog interfaces for position commands and sensor monitoring as well as SPI for real-time interfacing in demanding industrial and research applications.

Despite its small size and analog-controller price, E-709 packs a host of features formerly found only on much costlier digital controllers:

  • A 10W peak-power amplifier
  • TTL utility interfaces for synchronization, triggering and signaling
  • A built-in data recorder
  • An internal waveform generator

This is a true digital controller, with a digital servo based on sophisticated, real-time algorithms.  Beware the tendency of some to call any controller with communications interfaces "digital"!  In a digital servo, gains and other parameters are software-settable, and the system is immune to DAC drift since the DAC resides inside the servo loop.  And like all PI digital controllers, E-709 offers plug-and-play auto-calibration with our closed-loop nanopositioners.  It is available in versions for PI nanopositioners with capacitive sensors or strain gauge and piezoresistive sensors, for which it offers unprecedented 5th-order digital linearization.

An unpackaged OEM version offers great performance
and value, with significant supportability benefits
from the plug-and-play auto-calibration and
remotely-accessible, software-based filter
parameters and diagnostic tools.
The E-709's digital servo offers a fast 10kHz update rate and integrates not just one but two notch filters.  The importance of notch filters in providing responsive positioning performance deserves more mention than it's ordinarily given, as they desensitize the servo to observable resonances in the nanopositioner and its load and supporting structure.  This allows significantly higher gains to be safely employed, which translates directly into crisp performance.  All PI servocontrollers have notch filters; our digital controllers actually offer two.  (Surprisingly, despite the manifest benefits of notch filters in nanopositioning, they remain uncommon in the marketplace.)

E-709 runs on any 24VDC source, making it ideal for OEM applications.  In fact, an unpackaged version for OEM applications offers special cost-effectiveness.  OEMs will also appreciate the supportability benefits of the software-settable servo parameters and plug-and-play automatic calibration. Research and industrial users alike will appreciate its utilization of PI's General Command Set, so applications written for any PI controller may be readily adapted to E-709 and vice versa.  A host of software functionality is also supported, including comprehensive LabVIEW libraries and Windows .dll and Linux .so libraries.

E-709 is also ideal for autofocus applications ranging from research microscopy to industrial inspection, scanning and even the latest genomics applications.   For example, it interfaces in real time with Motion X's superb FocusTrac through-optic focus sensors, providing precise, stable snap-in on the order of tens of milliseconds.  It is compatible with our full line of classical PIFOC objective positioners and sample-positioning Z stages.  It provides responsive real-time tracking, and it supports PI's unique Fast Focus & Freeze capability, where the unit can be bumplessly switched from external (focus) sensor to internal (capacitive, SGS or piezoresistive) sensor, allowing precise, calibrated, stable motions with respect to the focal plane.

E-709 offers a peek at the future of nanopositioning today, at an affordable price.

More reading on nanopositioning.