ELECTRONICS - [Current Loop Recorder]
Many industrial systems are using current signals to monitor certain devices (like pressure sensors, gas detectors, temperature sensors, ...). The signal is transported over 2 wires. The advantage of using a current signal instead of a voltage signal is the current signal remains the same, no matter how long the wiring is. When you transport 20 mA over an electrical wire, you will be able to measure the same 20 mA at the end of the wire. No matter how long the wire is. If you would use a voltage signal, the signal would decrease because the signalling wire has an electrical resistance.
Many industrial sensors can output a current signal between 4 and 20 mA. 4 mA corresponds with the minimal measuring range, while 20 mA corresponds with the maximal measuring range. A signal lower than 4 mA could indicate an error. After all, the monitoring system has to be able to detect a broken sensor/ transmitter.
I have created a 4 - 20 mA datalogger which is build around the Velleman K8055 USB card. This recorder allows you to log a 4 - 20 mA signal from a sensor. You can setup the measuring range and measuring units so the recorder can be connected to any transmitting sensor. The image below is showing you a screenshot of the recorder. The X-axis corresponds with time, the Y-axis corresponds with the measured value. The recorder will show you a red line when the measuring signal was invalid (under 4 mA or over 20 mA). In this case the datarecorder was setup to show a pressure sensor with a range between 0 and 100 bar.
The datalogger also has a window to show the real time values. Here you can show the A/D value (this is the digital value read from the K8055), the corresponding mA signal, or the true value from the sensor.
The software is not published yet!