Phidgets Forums

I'm looking for a suggestion on the best way to get from a pressure sensor (10mv/V, 100mV at 10VDC) into a 1073 device (which is on my network and the reason it was selected in the first place).

I want to have the 1073 mounted about 40 feet away from the pressure sensor. Presumably to read the wheatstone brige type sensor I need a 1046 which outputs USB, or a DAQ1500 which goes to a VINT.

I think the 1046 plugs directly into the 1073, but that's too long a USB run??

The DAQ1500 needs a VINT hub but then I still have a cable length problem.

Any suggestions?

You're correct that 40' is too far for USB- it tends to max out at 5m (or 16'). If you use the 1046, your only option is to extend the wires between your pressure sensor and the 1046. If you use the DAQ1500, you can extend the wires of the pressure sensor, or you can use a longer Phidget cable between the DAQ1500 and the hub. We only sell Phidget cables up to 350cm (11.5') in length, but you can extend them by cutting the cable in half and soldering regular hook-up wire in between.

There are two things you need to watch out for when using long cables:

1. Voltage drop-off
The longer the cable, the higher the resistance. This causes the voltage to drop off over a distance. In the case of the pressure sensor wires, this isn't a concern because wheatstone bridge sensors need to be calibrated anyways, so any distortion from voltage drop will also be calibrated out. In the case of the Phidget cable, if the voltage drops too low it might not be enough to power the DAQ1500.

2. Interference
The longer the cable, the more surface area is exposed to external interference. This may not be a big issue if there aren't a lot of other electronics in the vicinity, but interference can often cause instability in your system. You can mitigate interference by using shielded cable and by keeping wires far away from the worst interference-causing devices.