Controller Electronics for Airflow Calorimeter and Associated LENR Setup Components

Attached are the schematics for the signal conditioning and control electronics for the LENR apparatus I'm building. There are three subcircuits: inlet/outlet temperature monitoring, fan airflow control, and a temperature controller that drives a programmable power supply. The last circuit assumes an IR thermometer or a high temp thermocouple controller with 0-20 ma current loop output. This is an industry standard. All the circuits have been simulated and appear to operate correctly. Depending on your particular setup some circuits may be of interest.

Jeff

Quote from AlainCo

Is it stupid to say others could be adapt it to waterflow calorimeter ?

maybe the LM sensors are not enough precise for liquid calorimetry ?
sure driving water "fan" may be a bit different too...

too bad I'm too busy to participate... 20 years ago...
best wishes.

Not at all. Sealed thermocouples are readily available, as are flowmeters. Both are available from the Omega Corporation which readily sells to amateur scientists, Being incompressible, liquids provide an easier environment for doing calorimetry since the volume remains nearly constant with temperature. If there is a phase change, such as boiling, then the problem becomes a bit more difficult as the heat of vaporization must be included in the calculations.

Quote from GlowFish

Looks great. Just some quick questions. Does the DAQ have its own input filter? Perhaps add small 10n cap and maybe a load resistor across the output of the Op-amps U1 and U2 and from the 7.5V to GND at the pins of the op-amps (U1, U2 and U3) to decouple HF noise especially if the DAQ is going to be at the end of a lengthy cable. The 7.5V reference is generated by a linear adjustable regulator which is source only so your 7.5V reference "sink" impedance is basically only your feedback network. Perhaps add a small 0.1uF ceramic in parallel with your output electrolytic to sink HF noise as C6 might have fairly high ESR. I also noticed that the LM317 regulator will only regulate properly if it has a minimum load of about 10mA. May I suggest R2 = 560 ohm and R1 = 110 ohm?

The DAQ has input filters but they are quite small to permit DAQ operation into the 10s of KHz. In the past I have run the DAQ without any additional filtering and have not encountered any noise problems. Most of the measurements are differential, so that helps, and I use shielded cables as well. Also the output voltages generated by the air flow temperature monitor and power supply controller circuits are scaled to give a 5V full scale output.

The LM317 requires that the load in parallel with the programming resistors sink at least 50 ua. The two load resistors I'm using total about 1460 ohms, so just the programming resistors, by themselves, sink ~5 ma. The values you specified would work also. However, I have since decided against using a floating 7.5V reference and elected to use +/- 15V supplies to the INA114 instrumentation amplifiers. That eliminates the need for the LM317. On page 4 the 7.5V reference is replaced by a precision 5.00V reference, REF02, manufactured by TI.

BTW,my day job is a signal integrity and microwave designer at Intel.

Quote from PetaLue

Your circuits are just looking fine. Can you please tell me the function of the IC IN11AP? Also tell me how you calculated the value of all resistors,i mean what parameters you consider here? What is the threshold level of all of your sensors? Are these circuits working efficiently?

The INA114 is a so called instrumentation amplifier. Internally it consists of three opamps with precision resistors in the internal feedback paths. This type of amplifier exhibits excellent common mode rejection, very high input impedance, and has the ability to set gain with a single external resistor.

Calculating the values of all the resistors would entail quite a bit of work on my side, since I did not commit all my design calculations to writing. Most of what you want can be obtained by examining the data sheets for the various integrated circuits. The same holds true for the sensor thresholds. Take a look at the LM35 data sheet. Regarding the temperature sense diodes, any book on solid state theory will give the diode junction vs. temperature relation. Gain for the two INA114p devices connected to the LM35 sensors was set to yield a ~5V dynamic range to the DAQ module. Gain for the other INA114s was set extremely high since they operate in a servo mode, where feedback is provided by an external input. The accuracy of the closed loop feedback system, in these cases, is a function of the difference between open and closed loop gains. Again, consult any good textbook on feedback theory for a more complete explanation.

I'm not sure what you mean by efficiently, but I have working examples of similar circuits used in a previous experiment. The circuits I posted have been simulated using HSPICE and appear to behave correctly. Some minor adjustments to resistor values may be required.

Jeff

The circuit boards arrived yesterday, and I assembled one last night. After making one minor circuit change and chasing down a cold solder joint (Do not attempt to assemble surface mount components with a soldering iron, no matter how fine a tip you may have.) the circuits work as designed. The thermal mass controller measures airflow by means of a pair of diodes, one with a resistive heater and one without. If you touch the cold diode it warms up, and the fan speed decreases. Similarly, if the heated diode is removed from the airstream the fan speed increases.

The next step is to connect all the sensors and the DAQ module and start performing calibration on an empty cell. This will give a baseline for power applied to the heater vs. air temperature rise through the calorimeter chamber.

Jeff