Looking for help on choosing pressure sensor/transducer

[Digital Corpus]

Hey all. I'm wondering you guys wouldn't mind assist with a decision I need to make for a project of mine. Because "it's been a while" since I've "dabbled" in electronics, I'm posting this here in the beginner forum...

Anyhow, here is the application I'm using the sensor/transducer in. It's a digital automotive gauge, data acquisition device, platform agnostic (don't care which car or gas/diesel engine type), that requires a large absolute pressure range, >60 psi-a, and decent accuracy, <=2%. Due to the complexity of the project, modular expansion et al., I'm trying to keep cost and complexity down as much as I can. There are two sensors from Honeywell that are up for consideration, the latter is new to the market since I started the project:
SSCSANN100PAAA5 <-- currently in the design
NBPLANN100PAUNV <-- alternative consideration

The cost difference is about $18 at 25 pcs or more which is about 20% the component cost. I prefer the SSC due to it's calibrated, compensated, simplistic implimentation, and ease of use in the project. It's be mounted on a side of the PCB for s slim profile.

The NBP is rated for the same accuracy for ~1/3rd the cost though requires additional circuity for stability and accuracy of the output signal. Also, I will only be able to mount it perpendicular to the PCB which *might* be an issue, though can be a good thing depending on the vehicle.

[Alexei.Polkhanov]

Both may not survive the toxicity of the environment in automotive application.

You probably need something like this: http://www.brinstrumentation.co.in/baumer-process-instruments.html#baumer-pressure-transmitter. It is will cost $150-350 each or more. If you use sensors with standard 4-20mA current loop interface they will be compatible with virtually any other automation piece of equipment like calibrators, PLCs etc, plus current loop permits different wiring without any adjustment. Well I am speaking from Control Systems engineer point of view so it maybe little overkill for your app but if you want to build serious, modular test gear that is the way to go IMHO and it won't require any electronics skills except maybe connecting some wires, but you'll need to program the controller that you use.

[Alexei.Polkhanov]

Good one on Ebay - http://www.ebay.com/itm/Burkert-430-452-S-Pressure-ECO-1-Transmitter-0-100PSI-4-20mA-10-30VDC-1-4-NPT-/400515388470?pt=LH_DefaultDomain_0&hash=item5d4093d436

[Digital Corpus]

I'll be needing those industrial types for oil pressure, though I did forget to mention that the pressures I'm current measuring are air pressures for turbo charged vehicles. With little effort, such as a bit of cotton wad and a 1" dia x 6" long coiled copper tube, it is easy to use such sensors to even measure the exhaust manifold pressures. Right now, warm air is the harshest environment I'll be measuring the pressure to since the length of hose/tube is too long for there to be any significant heat transfer.

[Alexei.Polkhanov]

I'll be needing those industrial types for oil pressure, though I did forget to mention that the pressures I'm current measuring are air pressures for turbo charged vehicles. With little effort, such as a bit of cotton wad and a 1" dia x 6" long coiled copper tube, it is easy to use such sensors to even measure the exhaust manifold pressures. Right now, warm air is the harshest environment I'll be measuring the pressure to since the length of hose/tube is too long for there to be any significant heat transfer.

The BAUMER one was for gas (air, or else). Perhaps you should try, but datasheet for those Honeywell piezo transducers warns against any corrosive environment - I guess they have membrane in there that can be damaged easily. I found one of those sensors in my sensor box - MPX2102ASX-ND, it looks pretty flimsy to me. Thing is that it gives you -+ voltage output, so you will have to calibrate it yourself somehow to get absolute reading.

With pressure transmitter (4-20mA output) you get one of these http://www.dataq.com/products/hardware/el-usb-data-loggers/el-usb-4-data-logger.html, connect 2 wires, plug in USB into laptop and you are pretty much done on hardware part :-) I am just saying.

[Digital Corpus]

I understand where you're coming from and yes, the environment around a car car be hazardous. However, it is fairly common in the initial community I'm developing this for to use cheaper sensors than what I've listed. As the stock vehicles have 8-bit AD for the sensors that range from 2 bar to 3 bar MAP (manifold absolute pressure), they sometimes need to be swapped out with ones of a greater range. A common one that is used with high reliability is the MPXH6400A. The stock sensors are basically these guys from Bosch.

In fact, I have one in my ECU as we speak and almost used it in the project. As there are no pinhole leaks, of gaps or not-completely-tight fittings when these upgrade are done correctly, there is no gas escaping from near the sensor so there isn't much of a possibility for hazardous material to migrate from the charge pipes to the sensor itself, especially since they are mounted at a higher point in the vehicle. If the end user of the gauge improperly installs it, then it will die. However, the user base this is going towards doesn't have that typical problem.

My initial community this is being developed for is the Volkswagen/Audi TDI, or turbo diesel, group. When these cars are modified, there is demand for high quality monitoring equipment. Some, but not most, will swap out the ECU in order to have a higher refresh rate, about 2.5-3.5 to 8+ samp/sec, when monitoring parameters via the OBD port, and also gain the ability to flash the ECU via the OBD port. What I'm building is DAQ that can log an order of magnitude faster, has greater precision, and can maintain that speed and precision upon all devices attached, which there are 6 common parameters are needed, but modular expansion puts this out to a total of 14 parameters.

Methinks I should have put this in the projects section at this point...

Long story short, The first sensor has one downside of it's cost and the second has the need for additional circuity and enlarges the profile of the final device.

[Spunky]

Not sure which companies trade in the US, but in europe Wika or Druck would provide probably the most precise and stable units (at a price), SensorOne usually have a large range, Jumo are usually among the cheapest but still good, and SensorTechnics are also quite reasonable. All sensor companies seem to be in germany and you always get the best price dealing direct with the factory not the local office.

Also try asking them so supply them bare (without housing, but with compensation and output circuits) as the housing and the cables are what drive the cost up.

To get a really good price you need to be looking to buy at least 100qty in each order, as almost everything in the low pressure range (under 60bar) is made to order, if you can get a quantity made in one production run the costs drop dramatically. Expect a lead time of 6 to 8 weeks.

For automotive use you probably don't need high accuracy. At 8 bit resolution 0.5% is all you could make use of anyway and that's considered fairly crude for a pressure transmitter so you should be able to get an ok price.

[Digital Corpus]

Thank you. I'll look into those companies and see what pricing they have. I've actually gone through and watched Dave's DFM videos, and most of those principles were a consideration already. Obviously I wasn't following every note, but the guidelines are pretty helpful. As such I was expecting to order a minimum of 50-100 pcs.

Anyhow, more names to look at, Wika and SensorOne seems to have readily accessible sites, so I'll see what options are there.

Due to the other peripheral requirements for my MCU, I happen to have one that has a 10-bit AD. For a 100 psi-a sensor, this gives me a resolution of about 6.7-8.4 mBar depending on if a sensor's FSS is 0-100% or 10%-90%. Stock ECU setup has resolution of 10.2 mBar w/ 8-bit resolution and a limit of 2.6 bar.

[Spunky]

If stock resolution on your input at 8 bit is 10.2mbar, and you add 2 bits, wouldn't that give you a resolution of around 2.5mbar? i.e. resolution x2x2 ?

[Digital Corpus]

If stock resolution on your input at 8 bit is 10.2mbar, and you add 2 bits, wouldn't that give you a resolution of around 2.5mbar? i.e. resolution x2x2 ?

...I happen to have one that has a 10-bit AD. For a 100 psi-a sensor, this gives me...

If I was using the stock sensor, yes you are correct.

However, I'm trying to build this with one sensor that will work for diesel and gasoline engines. Diesels tend to run higher pressures and some of them run variable geometry turbos. In order to properly "tune" these in the control software watching the back pressure, aka exhaust manifold pressure aka EMP, on the turbo in relation to the generated pressure for the engine to consume is an important metric. For higher end builds, this is easily in the 60 psi-a range. Add atmospheric pressure and you get about 75 psi-a. Since most sensors/transducers go from a max pressure of 60 psi and then to 100 psi, the latter is what I'm looking for. This is a little less than 7 bar.

The 100 psi-a part is about $30 or the other is about $10 and maybe $2-3 in additional circuit component costs. If the end user kills it with improper installation, it's a simple part to replace. I think I'm going to be going with the first choice. Despite the cost, it is a 4 pin package that is easily replaceable and takes up considerably less real estate space on the PCB, especially given that I don't have to include additional discrete components etc to have a valid output signal.