The input impedance is dependent on the programmed sample rate, the transmit rate, and how many and what type of sensors are enabled. As can be seen from the product datasheet, there are 3 different harvester/generator inputs, and a myriad of programmable operating modes to accommodate varied harvesters and energy environments.

The most commonly used harvester input is the Piezo input, an ultra-efficient switchmode converter. Figure 1 below clearly demonstrates the capability of the EH-Link™ versus different wireless transmit rates. Figure 1 shows test results where the aplied voltage was 7.5V, a 1000 ohm Wheatstone bridge is being measured, and the transmit rate and packet payload size were varied. In this test the sample rate is fixed at one sample per second. The number of measurements saved up for transmission was varied from 1 to 30, where at 1 a single measurement was transmitted over the wireless link once per second. At 30 in this test, 30 measurements are accumulated and transmitted every 30 seconds. This is done to demonstrate that much less power is used to sample than to transmit. It is important to note that even at 30, the data sample timing is preserved and no data are missed in the received measurement stream.

Another harvester input, the 'ultra low voltage' input, is very low impedance and is intended for thermoelectric generators and thermopiles, which have very low voltage and relatively high output current. The input impedance on this input is on the order of 6 ohms, and varies a little with operating mode. With our demo TEG harvester is able to sustain continuous sampling at 64 samples per second and one transmission per second with a temperature differential of only 8 degrees Celsius between the mounting surface and the heat sink on the cool side.

The third input is an ultra high impedance AC type intended for use with high voltage piezo materials where the capacitance of the piezo is discharged at a threshold of approximately 130V peak. This is done to maximize the 'V' term in the capacitive energy equation (one half C*V squared). This input is somewhat experimental but has been shown to be very high efficiency and very high (>1 megohm) input impedance before the discharge threshold is reached, making it ideal for use with high voltage piezo ceramics.

No, carbon fiber should pose no problem.

In most cases, MicroStrain calibrates every DVRT with its accompanying electronics and provides a detailed calibration certificate. The certificate provides 3 methods of calibration and all the particulars including formulas to resolve voltage into engineering units.

• Standard Least Squares Linear Fit provides a simple mathematical method to convert sensor output to displacement and delivers reasonable accuracy.
• Polynomial Fit provides a more mathematically intensive method to convert sensor output to displacement and in turn delivers a high degree of accuracy. A possible drawback to some users of this method may be that it can not accurately report measurements beyond its stroke length (i.e., over-stroking).
• Multi-Segment Linear Fit provides the most mathematically intensive method to convert sensor output to displacement, delivers a high degree of accuracy and is not subject to the drawback of over-stroking.

The output is an analog DC voltage proportional to linear displacement. The full scale voltage can be customer specified. The analog voltage is easily read using a multi-meter. The voltage can also be read in the digital domain by using MicroStrain’s smart motherboards. These motherboards provide a data gateway to PC-based software or to user-programmable LCD displays on the motherboards themselves.

Yes. A Micro-D connector with color-coded wire pigtail is provided and is designed to complete the run to a DAQ.

Yes. A comparison chart may be found at: http://files.microstrain.com/Displacement-Sensors-Comparison.pdf

Normally, every DVRT is calibrated at the factory with its accompanying DEMOD. The calibration is made over the entire system (DVRT and DEMOD) to insure the highest accuracy. DVRTs and DEMODS are color-coded to insure that they stay together as a pair when in use.

Both DEMOD-DVRT and DEMOD-DVRT-TC are signal conditioning cards designed to support MicroStrain’s DVRTs and many other types of sensors. Both cards contain all the requisite connectors to facilitate plug-and-play use, including: active, jumper selectable low pass filters, input supply line filters with reverse input protection, and output line buffers. The DEMOD-DVRT-TC specifically provides temperature compensated conditioning.

** Non-contact comes standard with threaded body.

DVRT (Differential Variable Reluctance Transducer) and LVDT (Linear Variable Differential Transformer) combined with their signal conditioners convert a linear displacement into a linear variable electrical output signal. The displacement is detected by the movement of a core within the coils inside of the sensor. The difference between the sensors is in their coil format.

DVRT: The coil shown below is energized using an AC excitation through the center tap. The coil is usually arranged in a Wheatstone bridge with the Center Tap being the bridge excitation (forming a "half bridge"). With the core in the central location (null) the signals Va and Vb are equal. When the core moves, Va and Vb vary proportionally. Since this design is less complicated we are able to produce considerably smaller sensors than LVDT manufacturers.

LVDT: The primary coil is excited with an AC waveform. When the core is in the central location, the coupling between the secondary coils (Va & Vb) and the primary coil Ve) is equal. When the core moves, Va changes proportionally to Vb in both magnitude and phase.

Our calibration is in Volts/Newton and the slope of the line is shown to be 0.6967 V/N (in this particular example).  If we tested the AIFP^® using the signal conditioner in our factory, the calibration is for testing purposes only and cannot be used as-is in your environment.  If we calibrated the AIFP^® with your electronics, the calibration could be used to convert the sensor output to Newtons (output Volts/0.6967 V/N). 

We do present some high level information on the AIFP^® in this presentation:

AIFP^® Presentation.

We also list a number of scientific articles on our web site that contain information regarding the AIFP^®: Scientific Papers

The AIFP^® should not be removed from the specimen by pulling on the sensor cable.  The correct way is to tie a suture through the hole in the metal substrate of the sensor and use the suture to pull the sensor out of your specimen.