Pressure And Linear Position Transducers

Hi !

I'm working on a universal testing machine (tensile strength) and I need to connect a linear position transducer and a pressure transducer to an Arduino which will eventually log to excel. I've tried to manage the electronic parts, but I'm not familiar with it.

So, my pressure transducer is 2 wires (supply + / -), Pressure Range 0-5000PSI G, Output 4-20mA. I know I'll use a 250ohm resistor. Model : M5251-000005-05KPG

For my linear position transducer, I got 3 wires, total resistance in ohms = 9000.
Model : Short Longfellow Series SLF06

Can someone help me with the wiring diagram ? How do I connect both to analog pins ?

Thanks in advance !

Looks good so far. I can give you two circuits: one will just work well enough to check that the sensors are working, the second will give you reasonable protection against errors such as plugging things in backwards. If you're just testing, use the first one. If you want this thing to last more than a year with inexperienced people plugging things in, then you want the second one. (A custom PCB is necessary for that level of reliability.)

To get data into Excel, there's a number of different methods. I recently came across PLX-DAQ Version2 which looks like it might fit what you want to do.

Thank you for your answer. The first one looks interesting. I never made a custom PCB, so I thought of using a breadboard for my tests. As you’ll see on the picture, I tried to sketch what I plan to do, but I really don’t know if it’s good or not. I didn’t even use the breadboard, but I plan to.

Plus, I already downloaded the PLX-DAQ, but I have the previous version so thanks to you, I’ll update it !

Tensile testers are fun, I've worked a lot with them. Most fun was drawing fibre reinforced epoxy pieces, they make a nice mess when they break.

One thing you have to look into is your pressure sensor. Tensile testers don't measure pressure, they measure force. We used to call these things "load cells" and they produce a reading in newton rather than PSI (which is force per area). PSI, or better: Pascal which is the SI unit, is force per area, and the area depends on the object that's tested. Therefore pressure doesn't make sense for a tensile tester.

Instead of a linear transducer, you can also use the screws that move your table to measure distance (at least I assume you go that way with the machine itself). Mechanical limit switches, after that it's a matter of counting (fractions of) rotation and you know exactly how much your table has moved. The speed of the rotation sets the speed of movement of the table. After all you don't normally care as much as where the table is, as you care about how much and how fast it moves.

Well done on the schematic. I like it!

You have one small problem - the linear position sensor “positive” should be connected to the Arduino 5V. The sensor is most likely a potentiometer. The slider will see a voltage that’s between the voltages applied to the + and - terminals. You must connect the + to the Arduino’s reference voltage. Otherwise your 12V supply may produce a little more voltage on a warm day and the output voltage will change. The Arduino 5V isn’t a stable reference either but the analog inputs on the Arduino are always a strict ratio of this voltage.

The 9000 Ohm resistor on your schematic should not be necessary.

I’m guessing a hydraulic piston is providing the tension force, so the pressure sensor will convert to tension force by simply multiplying by the piston area.

Hi !

The machine works with a hydraulic pump, and the measurements were taken with a ruler (well kinda), but now it's broken. The machine normally works with a pound dial and a lenght calculator, which will help find the modulus of elasticity and the breaking moment (fracture). Well, it's a really (really, really) brief explanation, but the point is that I will use the pressure transducer instead of my initial pound dial (which is broken anyway) and convert my results in excel after that.

(Sorry for the vocabulary mistakes, english is my second language.)


Thank you ! You've understand exactly what I'm trying to do ! But I just have one more question... Why is the 9000 Ohm resistor not a necessity in my schematic ? (mostly curiosity)

Because the position transducer is a resistor. Adding an extra resistor means the voltage of that end of the transducer is not known, unless you also measure that with another Arduino analog input.