Very cool. I'm familar with Honeywells SCX series pressure sensors. They seem a bit different though with positive and negative outputs as well as temp compensation. I found one of these in a highspeed centrifuge with vacuum system to reduce friction. But the unit had a small leak somewhere that would cause the unit to throw errors rendering it obsolete. So I placed the appropriate resistor across the sensor outputs to decrease overall output resistance = lower pressure. Got a few more years out of that centrifuge thanks to that mod!
the chip looks like a complex digital design, not analog at all, it's probably an ADC, fed into a LUT, fed into a DAC, hence the datasheet spec "12-bit". The unused pins on the package are probably the programming and calibration pins, where the factory can put in a custom LUT for each part. They probably made it that way to make it cheaper, as programming is easier than laser trimming resistors.
Used one differential, with range ±0.5 inch H₂O, 'reference' series, SPI output to build flow meter. ( Just piece of pipe with two perforation strips on the inner circumference at a specified distance to sense pressure drop, great stuff )
Pro tip when using ratiometric sensors such as pressure sensors and Hall sensors. Skip the expense of the precision voltage reference. These are designed to mate with ADC converters, where the voltage reference for the sensor and ADC uses the same varying reference voltage, so the ADC and sensor are both ratiometric, and as a result, cancels out the measurement error. Check the datasheet for this configuration. It is common for data collection using battery operated devices. It is reduced parts count wt;h the elimination of the voltage reference, and reduction of power use,
To me sensors are some of the most interesting parts as they are the interface to the real world (if such a thing exists). You could hook one of these up to an Arduino and see if you could measure barometric pressure changes over a protracted time span, or You could hook one of these up to a faucet to track water pressure, or Make a tire pressure gauge, or If you have forced air heating/cooling you could measure pressure differential across a filter to determine when filter needs to be changed, or .......
the port is open to the air, I assume the other side of the diaphragm is sealed (fixed at whatever the air pressure was when it was manufactured?) I did see some dual port units on the data sheet.. could be useful in some applications
@@zebo-the-fat Single port versions are always absolute, the reference is a very high quality vacuum sealed in during manufacture. dual port units have connections to both sides
You can get these with different sensitivities and configurations. I designed a water spray for coal trucks using one, where any vehicle that ran over a length of hose, (like the old hoses at a filling station), which was open on one end, triggered the sensor, and turned on the spray to keep down dust. The main challenge was the plumbing, to reduce a 3/4" piece of red hydraulic hose down to the size of tubing to fit the sensor.
All the no connect are there for use as a digital sensor, and to program the assorted variations for a zero point and a full scale, as the basic sensor itself covers the entire pressure span, so the variants are programmed in factory for a range, and this calibration is stored in the internal flash memory. Then there is a 12 bit DAC that uses the incoming pressure, likely converted by a 16 bit unit on the die, and the logic sea of gates there then does a temperature correction, thus 6 pins to the sensor die, 4 are for a ratiometric measure, and the other 2 are for a buried base emitter junction of a transistor on the die, used in conjunction with a bandgap reference on the main chip, to get a stable reference for the ADC, and a stable supply for the bridge as well. This then is scaled and temperature corrected ( ratiometric lookup to contract the scale, and then a sliding window for the temperature correction off a table in the flash on die) before going to the ADC to be sent out.
you can do a search: Piezo-resistive pressure sensors consist of a diaphragm - mostly made of silicon - with integrated strain gauges to detect strain as a result of applied pressure. These strain gauges are typically configured in a Wheatstone bridge circuit to reduce sensitivity and increase the output. Due to the material being used the pressure limitation is at around 1,000 bar.
How did you determine that there is a piezoelectric strain gauge to measure the deflection of the diaphragm? Silicon is not piezoelectric, though I suspect that a strain gauge could be fabricated on the back side of the diaphragm. Another sensing approach that is used in macroscopic high accuracy pressure sensors is to measure changes in capacitance between the diaphragm and one or two electrodes on the back side of the diaphragm. With a single electrode opposite the center of the diaphragm, the deflection is proportional to the square of the pressure difference across the diaphragm. If I remember correctly, with a pair of electrodes the change in the difference in capacitance can be linear with the pressure difference.
Thanks for ripping one open so we could see what’s inside 🙂
Such a complicated device, yet so easy to use. I like it.
Very cool. I'm familar with Honeywells SCX series pressure sensors. They seem a bit different though with positive and negative outputs as well as temp compensation. I found one of these in a highspeed centrifuge with vacuum system to reduce friction. But the unit had a small leak somewhere that would cause the unit to throw errors rendering it obsolete. So I placed the appropriate resistor across the sensor outputs to decrease overall output resistance = lower pressure. Got a few more years out of that centrifuge thanks to that mod!
the chip looks like a complex digital design, not analog at all, it's probably an ADC, fed into a LUT, fed into a DAC, hence the datasheet spec "12-bit". The unused pins on the package are probably the programming and calibration pins, where the factory can put in a custom LUT for each part. They probably made it that way to make it cheaper, as programming is easier than laser trimming resistors.
Used one differential, with range ±0.5 inch H₂O, 'reference' series, SPI output to build flow meter. ( Just piece of pipe with two perforation strips on the inner circumference at a specified distance to sense pressure drop, great stuff )
Wow the magnification is amazing. So interesting to see inside
Pro tip when using ratiometric sensors such as pressure sensors and Hall sensors. Skip the expense of the precision voltage reference. These are designed to mate with ADC converters, where the voltage reference for the sensor and ADC uses the same varying reference voltage, so the ADC and sensor are both ratiometric, and as a result, cancels out the measurement error. Check the datasheet for this configuration. It is common for data collection using battery operated devices. It is reduced parts count wt;h the elimination of the voltage reference, and reduction of power use,
To me sensors are some of the most interesting parts as they are the interface to the real world (if such a thing exists).
You could hook one of these up to an Arduino and see if you could measure barometric pressure changes over a protracted time span, or
You could hook one of these up to a faucet to track water pressure, or
Make a tire pressure gauge, or
If you have forced air heating/cooling you could measure pressure differential across a filter to determine when filter needs to be changed, or
.......
the port is open to the air, I assume the other side of the diaphragm is sealed (fixed at whatever the air pressure was when it was manufactured?) I did see some dual port units on the data sheet.. could be useful in some applications
@@zebo-the-fat Single port versions are always absolute, the reference is a very high quality vacuum sealed in during manufacture. dual port units have connections to both sides
You can get these with different sensitivities and configurations. I designed a water spray for coal trucks using one, where any vehicle that ran over a length of hose, (like the old hoses at a filling station), which was open on one end, triggered the sensor, and turned on the spray to keep down dust. The main challenge was the plumbing, to reduce a 3/4" piece of red hydraulic hose down to the size of tubing to fit the sensor.
All the no connect are there for use as a digital sensor, and to program the assorted variations for a zero point and a full scale, as the basic sensor itself covers the entire pressure span, so the variants are programmed in factory for a range, and this calibration is stored in the internal flash memory. Then there is a 12 bit DAC that uses the incoming pressure, likely converted by a 16 bit unit on the die, and the logic sea of gates there then does a temperature correction, thus 6 pins to the sensor die, 4 are for a ratiometric measure, and the other 2 are for a buried base emitter junction of a transistor on the die, used in conjunction with a bandgap reference on the main chip, to get a stable reference for the ADC, and a stable supply for the bridge as well. This then is scaled and temperature corrected ( ratiometric lookup to contract the scale, and then a sliding window for the temperature correction off a table in the flash on die) before going to the ADC to be sent out.
this is exactly what I was thinking when I saw the die and reference to "12-bit" in the datasheet
@1:05 pee·ay·zow, not pee-zeeyow 😉 Love the video as always, always looking forward to the next. Keep up the good work!
A nice sensor indeed.
It is made from quarts with a flex resistor painted on top..
you can do a search:
Piezo-resistive pressure sensors consist of a diaphragm - mostly made of silicon - with integrated strain gauges to detect strain as a result of applied pressure. These strain gauges are typically configured in a Wheatstone bridge circuit to reduce sensitivity and increase the output. Due to the material being used the pressure limitation is at around 1,000 bar.
How did you determine that there is a piezoelectric strain gauge to measure the deflection of the diaphragm? Silicon is not piezoelectric, though I suspect that a strain gauge could be fabricated on the back side of the diaphragm.
Another sensing approach that is used in macroscopic high accuracy pressure sensors is to measure changes in capacitance between the diaphragm and one or two electrodes on the back side of the diaphragm. With a single electrode opposite the center of the diaphragm, the deflection is proportional to the square of the pressure difference across the diaphragm. If I remember correctly, with a pair of electrodes the change in the difference in capacitance can be linear with the pressure difference.
you can make a strain gauge with polysilicon resistors on a die with the same process a regular chip is made
Does it do negative pressure (vacuum) ?
Nifty.
Very cool :)