Cbart42 wrote: ↑
Tue Apr 30, 2019 2:02 pm
I am fairly new to Pi usage and want to do a Pressure logging project to sense and record pressures over time from a set of Pressure Transducers (0-3000PSI). The logger will need 2 sensors to be recording pressures from seperate banks either by same Pi or one for each side. Whichever way works best. The desired transducers come in the following options which would work best for Pi connection and recording? I was thinking the 624 as it could be powered directly from Pi 5v pin (I think) but unsure if that's best route or using one of the others. Any suggestions would be greatly appreciated. Not sure exactly what else I will need to get desired logging from sensors.
625 (2-wire): 9 to 28 VDC
623 (3-wire): 9 to 30 VDC
624 (3-wire): 5 VDC (fixed)
626 (3-wire): 14 to 30 VDC
627 (3-wire): 14 to 30 VDC
625:Output: 4 to 20 mAFull scale output: 16 mA ± 1%Zero output: 4 mA ± 2%
623:Output: 0.5 to 5.5 VDCFull scale output: 5.0 VDC ± 1%Zero output: 0.5 VDC ± 2%
624:Output: 0.5 to 4.5 VDC ratiometricFull scale output: 4.0 VDC ± 2%Zero output: 0.5 VDC ± 2%
626:Output: 1 to 11 VDCFull scale output: 10 VDC ± 1%Zero output: 1.0 VDC ± 2%
627:Output: 0 to 10 VDCFull scale output: 10 VDC ± 1%Zero output: 0 VDC ± 2%Supply Current:15 mA maximum (no load)
I would choose the 624, and look for a suitable ADC hat or I2C board that can range 0-5VDC. The measured range 0-3000PSI is a wide range and depending on the accuracy needed go for an ADC with at east 16-24 bits of resolution.
With these sorts of transducers the quality (cleanness) of the supply voltage is critical, be sure to implement the suggested power supply conditioning and filtering circuit recommended in the Data Sheets.
Always consider over pressure events. Although most of these style of transducers have a 10x burst pressure, anything over 150% of FSD usually damages the sensor, or at least will require you to re-calibrate.
Also, depending on what you are doing with the pressure reading, temperature compensation may be required. I am not sure of these pressure sensors are temperature compensating. Even if they are, they are usually only able to compensate internally for a moderate temperature range, beyond that you need to externally compensate in H/W or in the S/W.
Example: if your are trying to determine the volume of compressed air in these banks, based on the water capacity of the storage tanks and the fill pressure, due to Gay-Lussac's Law: The Pressure Temperature Law, you will need to correct for pressure increases due to higher temperatures. Gay-Lussac's Law: states that the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature.
Temperature compensation for liquid media is less of an issue. However most if not all mechanical style sensors (as is the 624) are calibrated for a given temperature (usually 20º or 25ºC) so if accuracy is your thing, and the environment (or media) is outside the 624's calibration temperature, then you may want to include a temperature sensor as well.
Please let us know more about the application, as when you mention 3000PSI and 'banks' I am lead to think its a diving/medical air/gas application, which my many years in the Navy have given me a great interest.