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Can you feel the Pressure? A Pressure Sensor Comparison

Pressure sensors Volume

Volume measurement is one of the features that really sets BrewTroller apart!  The way this is accomplished is via the use of pressure sensors.  

This is really a pretty simple proposition.  Any BrewTroller board can handle an input on the analog inputs of 0-5 volts for volume measurement.  This really leaves it up to you guys, the users, to determine how they want to accomplish this.  

Freescale MXP5010

The "Standard" the has been used widely for a number of years is the Freescale MXP5010 sensor.

MXP5010 Specs:

Pressure Range  0-10kpa
Supply Voltage 5 volts
Signal Range 0-5 volts
Max Temp 80c
Accuracy 5% (@min voltage)

 

These sensors are not rated for contact with liquid, so a tube is used between the sensor and a measuring port or dip tube.  The theory here is that the pressure of the liquid on the air trapped in the tube or dip tube would be sufficient to measure the pressure and volume in the kettle.  The first tests done on this setup were done and readings were good.  But it was quickly discovered that changes in temperature were affecting the volume of air trapped in the tube.  

Basically, as the air in the tube heated up (say in a dip tube in the liquid itself) it would expand, pushing a bubble of air out of the tube.  Since air is compressible, if the volume of air changes, so would the pressure sent to the sensor itself.  This throws the calibration and accuracy off. 

So, to solve this issue, an aquarium or air pump was placed in to the mix via a T-fitting and an air valve to control the volume of air coming from the pump.  This kept the volume of air consistent in the tube, and the pressure would read correctly. 

Example:

The person setting this up would adjust the flow of air so that it was just a couple of bubbles a second.  The BrewTroller would average the readings over time to even out the ripple effect from the extra air being added to the tube.

This kind of setup works, but its finicky, requires adjustment, and extra equipment.  Some users have reported that the air pumps can be electrically noisy as well, causing issues, though this doesn't seem to be common.  

In reality, this kind of setup is ideal for direct fired kettles, as you can run a dip tube from the top of the vessel, and not be close to the eat with your sensor or tubing, preventing heat related issues.

DingTek DP200

In an effort to solve some of the issues, and simplify pressure sensor readings, some users, and the owners of BrewTroller (me) started to look for other solutions, and in steps the DP200 from DingTek

DP200 Specs

Pressure Range  0-10kpa
Supply Voltage 12 volts
Signal Range 0-5 volts
Max Temp 160c
Accuracy .03% (per degree C)

 

This sensor solves a few issues, but presents a couple of its own.  First off, it eliminates the need for tubing, air pumps, air valves, and dip tubes.  Second, its capable of temperatures above boiling, and can directly contact the liquid in your kettle. 

The person setting up this system would drill or punch a hole in their kettle as low as possible

On the bottom of the kettle is the ideal spot.  Again, no tubing or any kind of air buffer is needed here.

The downside to this setup comes when you are looking at a direct fired kettle.  You can't mount this sensor in the flames, so the bottom won't work.  And, unless you can effectively shield the sensor, on the side near the bottom could be problematic as well.

One final note, these sensors need a 12v power source, so you will power them off your 12v power supply and not off of the BrewTroller Board

Similarities 

Now that we have looked at 2 options and their differences, lets talk about their similarities!  Both sensors put off 0-5v as their signal, and both will connect to the same analog input on the BrewTroller board (any of those inputs).  Then, in the firmware, you will calibrate the same.  Generally, you go into the calibration screen, add a gallon of water and grab a reading, then add another and grab a reading.  Continue for as many gallons as you want or need.

Conclusion

Both of these sensor options will allow you to monitor volume in your vessels, and therefor add a whole new level of automation to your brewery!  Each has their strengths and weaknesses, or pros and cons, and I've summed those up here:

Sensor  Pros Cons
MXP5010 Inexpensive
Current Standard
Used by a lot of people
Works well with Direct Fired Vessels
Requires Tubing
Requires Air Pumps
Not Liquid Capable
Not capable of high temp
DP200 Easy to Setup
Direct Wort/Liquid Contact
No Air Buffer
Expensive
Difficult to use with Direct Fired Vessels
Few users (currently as of April '17)

 

If you are wanting to use this awesome feature of BrewTroller, pick up some sensors today and get them hooked up!

Links to Buy:
DP200 Pressure Sensor (Currently a Pre-Order)
MXP5010 (from widgeneering.com)

If you want more information on volume measurement, check out our Volume Measurement Page

If you have any questions about this, please let us know!  I hope this was helpful!



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