thank you so much for your suggestionYes, I have plenty of ideas. Since you mention NPT fittings I will assume you are looking at engine temperatures such as coolant? My choice for a sensor based on your applications would likely be Type K thermocouples with a stainless steel sheath material. Choose the length and diameter based on your needs. Next based on the sheath diameter you use a compression coupling which are very common and come in about any NPT size you want. Anyway for NPT you want to use a compression fitting. Just as an example when considering sheath material for a sensor since you mention a marine application if you are sensing coolant temperature if the coolant is for example sea water you want a sheath resistant to salt water unless you are on the Great Lakes where salt corrosion is not a problem.A Google of Thermocouple and RTD compression fittings will more than get you started. All you need to know is your sheath diameter and NPT pipe diameter.
Since you already have apparently a 4 to 20 mA loop I am guessing you already have your sensor choice done.
The reason you see numbers like 4-20 mA, 1-5 volts and 2-10 volts is those are popular industry standards but also require a 24 VDC supply which you don't have. Again my choice of sensor would be a thermocouple. Next you need a transducer which just means a way to get from what you have to what you want. A Google of thermocouple amplifier will bring up a dozen small boards for thermocouple amplification which run on 5 VDC and give an amplified output proportional to temperature. You run off your thermocouple using thermocouple extension wire. You get your 5 VDC using a common buck converter get it now. You already have your A/D.
This is merely how I would approach things as to monitoring engine parameters as to temperatures. If you want pictures or links to anything I have suggested just ask.
Now if that's all done I would as suggested just use a 500 ohm 1% resistor in your 4 - 20 mA current loop which gives you 2 - 10 volts and program your CAN J1939 for an analog 2 - 10 VDC analog in and scale it to your temperature range for your dashboard display. Accuracy is a qualitive term and means little less being defined.
I have tried to keep this all modular using off the shelf modules in an effort to make things simple and easy. There is no shortage of published schematics out there if you choose to roll your own.
Ron
