Gen 5/Optima: Setup and Optimization

Technical Note
Gen 5/Optima: Setup and Optimization
The following document describes the available settings of the Gen 5/Optima amplifier (sections 1 and
2) and how to optimize these settings for a given application (section 3).
Digital Outputs – There are three selections for the USB digital output units. The choices are metric,
English or bits. If the units are English or metric the data is fully conditioned (recommended, see details
below). If bits are selected the data is not conditioned (this is not recommended for typical operation)
Analog Outputs – The analog output full scale range is +- 5 volts. The two conditioning selections are
Fully Conditioned and MSA 6 Compatible. Fully conditioned is the recommended choice, with all Gen 5
signal conditioning features enabled. The Optima’s analog output MUST be Fully conditioned.
Fully Conditioned
In the fully conditioned mode, the platform’s calibration matrix is automatically applied to the signal;
therefore crosstalk corrections and sensitivities are handled by the Gen5/Optima. The fully conditioned
mode also accounts for voltage drop along the length of the cable and uses actual excitation and gains
determined through calibration of the amplifier, not simply nominal values, to perform computations.
The Gen5/Optima allows you to define the working range (Amplifier Range) of each channel by adjusting
the individual Excitation voltages, Gains, and Zero Setpoints until the Amplifier Range is appropriate for
your application (see Configuring the Gen 5/Optima for Optimal Mechanical Range).
In the fully conditioned mode, you can also optimize the Analog Outputs (if using) to match your
Amplifier Range by adjusting the Analog Sensitivities (see Optimizing the Analog Outputs (fully
conditioned mode) below). In this mode converting the output voltage (±5 V) to the chosen engineering
units (N/Nm or lb/in-lb) is accomplished by simply dividing each channel’s analog output (mV) by its
user-defined Analog Sensitivity. This is the only computation required since the Gen5/Optima has
automatically applied the calibration matrix and accounted for the selected, Gain, Excitation voltage and
Zero Setpoints.
When using the digital output, the signal is already converted to the chosen engineering units (N/Nm or
lb/inlb) and will fall within the Amplifier Range. Analog Outputs and Analog Sensitivities are irrelevant.
MSA 6 Compatible (Gen 5 only)
The MSA 6 Compatible choice was developed for people familiar with the AMTI MSA 6 amplifier who
wish to use the Gen 5 in the same way (not available for Optima users). When running in MSA 6
Compatible mode the Gen 5 analog output range is +- 5 V. Individual excitation voltages, gain
amplifications, and zero setpoints can be adjusted to define the working range of the force sensor
(Amplifier Range). However, the calibration matrix is not automatically applied, nor are the amplifier’s
calibrated gains and excitations, and voltage drop along the cable is not accounted for. The user must
apply this conditioning manually.
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Amplifier Range - The Amplifier Range is the full-scale output range available for all digital and analog
output under the current configuration. Maximum and minimum values are displayed for each channel.
These values are functions of the Gen 5/Optima electrical output range and the selected channel
excitations, gains and setpoints. The range will update automatically if the settings are changed in the
Current Configuration group of the dialog box and the Apply button has been pressed. The Amplifier
Range should be optimized for the range of forces expected during the application being tested (see
Configuring the Gen 5 for Optimal Mechanical Range)
Analog Outputs – The values listed in Analog outputs depend on output mode. If the analog output
mode is set to MSA 6 compatible the Analog Outputs will not be visible and the output range will not be
adjustable and will be identical to the Amplifier Range.
For fully conditioned analog outputs (recommended) the ranges are determined by the Analog
Senstivities. The Analog Sensitivities determine the output millivolts per unit of mechanical load for each
channel. To exploit the full Amplifier Range while maximizing resolution, the Analog Sensitivities should
be adjusted until the Analog Outputs closely match the Amplifier Range (see Optimizing the Gen
Configuring the Gen 5/Optima for Optimal Mechanical Range
For best results the Gen 5/Optima signal conditioner should be setup to achieve both the highest
possible signal to noise ratio and maximum system resolution. This is accomplished by independently
configuring each channel. The three adjustable configuration settings that affect the measurement
range are excitation voltage, amplifier gain, and zero set point.
To achieve the best signal to noise ratio you want the Gen 5/Optima to output the largest possible
excitation voltage. This will normally be 10 volts; except for the most thermally variable conditions.
Under those conditions a lower excitation might be required to minimize thermal drift.
To achieve the best system resolution, apply the largest gain setting available where the Gen 5/Optima
measurement range is greater than the expected application range. By strategically utilizing the Gen
5/Optima Zero Setpoint feature to offset the Gen 5/Optima measurement range, a higher gain than
normal can occasionally be accomplished.
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The figure above shows the portion of the Amplifier Configuration dialog box used for configuring
measurement range. You can access this window through NetForce under Setup, Hardware installation,
Modify, and then by clicking on the Configure button next to the list of installed amplifiers.
Each channel’s Amplifier Range is a function of the excitation, gain, and zero set point selection
displayed in the combo boxes below it. To modify the amplifier ranges simply choose your selections
and then press Apply. Pressing Apply will download the new setting to the signal conditioner and update
the Amplifier Range on the display. Press Save in the main AMTI System Configuration window to save
these setting to the amplifier for future use.
To optimally configure the Gen 5/Optima, start with an initial excitation setting of 10, a gain of 500, and
a zero set point of 0. If the amplifier range is greater than the expected applied load range increase the
gain to next level and continue to do so until you discover the largest gain you can apply and still
encompass the expected applied load range for that channel. You will get a better signal to noise ratio
using 10 V of excitation, rather than a lower excitation and higher gain.
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Optimizing the Analog Outputs (fully conditioned mode)
If you are using the analog output from the Gen 5/Optima, after the optimal Amplifier Range has been
defined, the Analog Outputs should be optimized. This option is only present in the fully conditioned
mode. The Analog Outputs are dependent on the user-defined Analog Sensitivities. To modify the
Analog Outputs, change the Analog Sensitivity for the corresponding channel and press Apply. The
display will update to indicate the new Analog Output range.
To optimize the Analog Outputs, adjust the Analog Sensitivities until the Analog Outputs match the
Amplifier Range relatively closely. If the Analog Outputs range is much smaller than the Amplifier Range
you will not be able to reach the highest capacity indicated in your Amplifier Range. If your Analog
Outputs range is much larger than the Amplifier Range, you are not using the full output voltage range
of the amplifier; therefore you will have less resolution.
Make sure that you hit Apply before closing the Amplifier Configuration window, and then press Save in
the AMTI System Configuration window. Apply will allow you to see the computations based on the
current settings, and save will save these setting to the Gen 5/Optima for future use. If you do not click
save then next time to amplifier is powered on the last saved settings will be used.
In the fully conditioned mode you simply need to divide the output voltage (mV) by the Analog
Sensitivity you defined for each channel to convert your signal into engineering units (N/Nm or lb/in-lb)
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