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Here I will be presenting a thermal bridge balance method of power assessment for devices purporting to be generating excess heat over input power and thus COP>1.
Since the greater percentage of output of a DUT will be thermal, it is sensible to measure the unknown power output against a control of known power.
Think of it as an old fashioned balance beam scale where the unknown weight is put on one side, and compared to a known weight on the other side, but in this case we are "weighing" power.
The "null" balance technique is very robust and it's duality also cancels some common errors as is well known from bridge measurement techniques..
The method is simple. The DUT is put into a chamber with fixed thermal losses to ambient. It is allowed to run normally and a temperature rise above ambient will at some point stabilize.
This method automatically takes all power losses in circuitry as well as output power into account, without complicating measurement.
This stabilized temperature will be the setpoint for a power resistor in a second identical chamber which is servoed to the identical temperature. A PID (Proportional, Integral Derivative) control algorithm will maintain tight control of the servo loop.
This method eliminates the need for computation of crest factors which might be out of range for some digital instrumentation, and computational errors due to noisy breadboards or probe placements etc.
The control loop will be performed by DASYLab, a 32 bit PC control program. Temperature data will be acquired using matched type T thermocouples and an I / O Tech Shuttle Data Acquisition system. The system has excellent temperature stability, utilizing a isothermal block for reference junction compensation and seems to be stable to a fraction of a degree.
Balancing power will be computed in the control and will mirror the DUT exothermal response.
This thread will be locked until the complete method is presented, then will be opened for questions / comments / suggestions.
An outboard comments thread will be initially provided, then later moved to the main thread.
« Last Edit: 2011-01-28, 23:24:23 by ION »
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Topic: Thermal Bridge Test Method (Read 1191 times)
