Download AJ Pikul (EE) - ECE Senior Design

University of Connecticut
Department of Electrical and Computer Engineering
ECE 4901: Fall 2015-Spring 2016
Team 1606 (Phonon): Current Monitor System
AJ Pikul (EE)
Barath Parthasarathy(EE)
Jason Stock (EE)
Maya Dubrow (EE)
Sponsor Contact Information
[email protected]
Statement of Need
Phonon Corporation has tasked us with
the development of a calibrated DC/RMS
Main Required Electrical Parameters:
current measurement system to test their
Surface Acoustic Wave (SAW) devices. The
Calibrated measurement of DC and PWM current.
current measurement system will attach to a
Self-powered range of 5-50V (preferable 28V).
power source in order to compile calibrated
Low output impedance < 10 ohms.
measurements of DC and PWM (RMS) current
for SAW devices. In addition, the current
system should have an increased voltage range,
while maintaining low impedance. The focus should be on developing a flexible device which can give,
calculate, and track accurate data.
In addition to the basic design, we are also tasked with adding additional design features should time
pertain. These new features include intermittent current detection, voltage sensing, and a range selector to
record data at different time ranges to track errors. The project will encompass circuit building hardware
component with a software component which will be used to gather data.
This project is important for improving upon the testing equipment to better track current while
working with SAW technology.
Specs/ Capabilities of Current Model
Past Model:
This was our initial design for our project; it was fairly complex and would take a fair amount of
work to implement. The power supply circuit, which is outlined with a red box, consists of a
rectifier, three series zener diodes, and a voltage regulator circuit. These components would act
together to power our INA169 op-amp. The op-amp amplifies the signal and sends it to the output
circuit, which consists of an output impedance, and a buffer circuit. This buffer circuit is another
op-amp which was intended to keep the gain of the INA169 constant no matter what sense
resistance the current is flowing over. The point of the sense resistances is to incorporate ranging
into our project, such as the ranging feature on a multimeter. This is done by using four solid state
relays and four resistors of values 0.05, 0.1, 0.25, and 0.5 ohms for our different current ranges.
Each current range corresponds to a resistance value and a solid state relay. The relay allows current
to pass through the resistor, and the idea here is to have a constant voltage drop across all of the
resistors so we can get an accurate current sense reading once the signal goes through the op amp.
Current/Updated Model
Phonon’s original specifications
were to have a voltage range from 5-50V
and a current range from 0-10A. This made
things a bit more difficult for us in terms of
our system being able to handle that much
power. After a brief video conference with
the company, they altered their
specifications to make it a bit more realistic.
Now we have a voltage range from 5-30V
and 0-5A, which makes life much easier for
us. This is an updated and modified version
of our project, which is a lot less complex
and easier to work with. One of the main
parts of this circuit is that we took out the
entire power supply circuit because we
learned that the op-amp will be powered by
the signal we are measuring, which
simplifies the circuit. This schematic does
not have the ranging portion included in it,
but it will still be included. We modified the
ranging circuit to include MOSFETs in series with the resistors to utilize the low gate voltage aspect
of the opto-isolator and the high gate current capabilities of the FET to pass current through the
resistor. We are looking at testing the LTC6101 op-amp and using that as opposed to the INA169, if
the LTC6101 works, it will be able to make our project much more efficient. The DUT (device
under test) is connected to the op-amp, which will amplify the signal, and then from the op-amp, the
signal goes right to the DAQ, where all of the measurements will be taken, and stored for a short
amount of time on the computer.
Alternative Designs
The ranging circuit allows us to control the current over our op-amp which will then give
our DAQ a higher resolution. The two ranging circuits we are considering are parallel resistor and
series resistor setups. The series resistor setup would allow us to use a few less resistors, but also
has some unwanted resistance from MOSFETs that would cause voltage drops we could not ignore
since we are using very small resistances. The parallel setup has a low impedance so it will drop less
voltage which is useful to us. Within the parallel setup we can either use one op-amp over the whole
circuit, or one over each resistor. We chose to put one at each resistor because the switches change
resistance based on temperature, and with an op-amp over each separate resistor this change in
resistance can be ignored. This option is less cost-effective, but is more useful for a circuit that we
do not need to mass-produce.
We have chosen three options for our op-amp, and have tested one in our circuit. The first
we tested was the INA169 which is the updated version of the op-amp used by Phonon, the
INA139. This op-amp only operates properly at a high-side voltage of at least 3V, and the range for
the sense voltage is very low, at 100-500mV, which requires a buffer circuit to make sure the sense
voltage stays within that range. Our other two options for our op-amp are the INA282 and the
LTC6101. The INA282 is a better option than the 169 because it allows a sense voltage of up to
10V, which means it would not require a buffer circuit, but it does require circuit ranging up to 18V.
The LTC6101 has the largest input range of the three, and would also not require a buffer circuit. It
has an adjustable input impedance, a plus because low impedance is one of our given requirements,
and and very low offset voltage. We need to do extensive testing on the INA282 and the LTC6101
to further characterize these two op-amps and decide on one of the three for our circuit.
Benefits of Current Model
The specifications of this project required a current monitor with a large self-powered
voltage range while maintaining a low impedance. The purpose of this project is to improve upon a
previous current monitor. The first iteration of this circuit by Phonon used an INA139. While we
are still in the testing process, all of our options, INA169, INA282, and LTC6101, all have much
larger common mode voltages. This allows for power supply to use a larger range of power sources,
to make our circuit more flexible. The current circuit model also allows for a .1 mA resolution for
the 5 A range.
One of the bigger upgrades to our circuit takes place in the software component. Using
Visual Basic in combination with a DAQ, 1408FS, we developed code that would compile current
measurements from our circuit. The software is impressive as it track number of samples, as well as
the index sample at a very fast rate. Even more impressive, the data is being stored in binary in a
separate excel document. While the binary is not useful on its own, if converted can create and store
the data while still maintaining real time tracking of errors.
Budget/Component List
Note: Separate colors represent alternatives. The cost of the final product will only use one of these.
The total below is including all three of them to accurately represent the total cost of this entire
design iteration.
The buck-boost power supply was designed using TI.com’s workbench program which can
computationally design buck-boost accuracy. It was then verified by the engineers. The current
guard is used to protect the main sense amplifier, and the resistors change based on the maximum
ratings of that amplifier. The range station is the most complex design consideration and involves
range resistors, MOSFETS, SSR’s, and one high voltage gate driver to change the circuit being used.
The amplifiers are described above. The output circuit is used to provide a second stage
amplification to utilize the full range of the DAQ and to sum all the sense amplifiers. Summing all
the sense amplifiers as opposed to using multiplexers is a theoretical design which should work
because any sense amplifier switched “off” should have a 0 output. Using a summing amplifier over
a multiplexer reduces cost, incorporates two functions (gain and mixing) in one, and reduces latency.
Timeline
Some of the highlights of the first semester include creating a base for our project. The base
will be changed slightly to account for different op-amps to finalize a “best” option. In addition, the
software has been put in a good prototype state, where it can track the data consistently which was
the end goal. Despite this, we will still improve upon it to make it optimize the full capability of the
DAQ. On a less technical side, all paper and written requirements were also handed in on time, with
constant updates being streamlined using our website, google drive and Facebook group.
Looking to the future, we want to make
sure the power source can be programmable while
also ironing out any kinks with our current data
acquisition code. While simulating the device may
be difficult, we should still create a professional
outline with data from our extensive testing on
individual op-amps.
Future Plan Reiterated
As stated previously, we still have much to do in terms of testing and fine tuning our circuit to make
sure it is up to the standard of Phonon and a good representation of student from the University of
Connecticut. Our final To-Do list include:
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Spice Model and possible simulation.
Decide on specific resistance values.
Prototype and characterize LTC6101 and compare it to INA169.
Prototype varying DUTs.
Ranging options need to be tested.
Extensive testing!
Acknowledgements
We would like to thank Phonon for tasking us with this project, and to the University of
Connecticut for allowing us an outlet to work apply engineering concepts. Special thanks to Dr.
Gokirmak for meeting with us every week to go over project progress. And special thanks to Lam
Dinh, Paul Rago, and Scott Kraft for providing us with all the components and being very active in
helping/ guiding us in this project.