Conversion method from mA reads to specific Unit for data logger probe? - LabCollector

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SUMMARY:

For data loggers that sense Temperature and pressure, require a formula to be calculated for translating accurately the information coming from sensors and passing to analogic extension via data logger and finally to the add-on. This formula needs to added in Data logger add-on settings as explained in below sections.

Be Careful note
Depending on the probe, the sensors may or may not require the analogic extension.
This Knowledge Base for formula is ONLY for probes requiring analogic extension!

 

1. Choosing a 4-20mA signal over 0-10V

2. Formula for determining the current value in probe

1. Choosing a 4-20mA signal (over 0-10V)

Warning
We do not use the 0-10V for the calculation.

 

  • Choosing the mA current is important because the logger, sensors and its detectors need to be protected against high current.
  • Between the 4-20mA and the 0-10V, the 4-20 will allow you to be constant over large distances between the transmitter (measuring device) and the receiver (PLC-Programmable Logic Controller) while the current (0-10V) will decrease according to the distance. Also to note that the current does not “drop”, even if the length of cables is over miles.
  • The current on the other hand, gives its energy to the current loop.
  • Current is important if the resistance due to the cable and due to the various devices (display, remote management,…) is big.
  • A malfunction of one of the devices in the loop can be detected immediately if the signal reaches 0 mA. (Damaged cable, lightning strike or overvoltage which damages an element of the loop,…)

2. Formula for determining the current value in probe

  • You need to add the formula in DATA LOGGER -> SETUP -> LOGGERS SETUP -> CLICK ON THE PROBE YOU REQUIRE

 

 

 

  • Go to PROBE MA OPTIONS


 

  • For an example, in the below CO2 probe image:
    • 0mA = 0% CO2
    • 20mA = 10% CO2
    • 0% CO2 = 0 ppm (parts per million)
    • 10% CO2 = 100000 ppm

 

 

  • So the current value is used to determine a parameter (temperature, CO2 rate, etc):
    • 4 mA is the minimum
    • 20 mA is the maximum
  • The terminals are determined by the sensor.
  • So we have 1 equation for converting mA in ppm for CO2 detection, by calculating Y = A*X + B where
    • X = x-axis
    • Y = y-axis
    • A =
    • B = ordered at the origin
      • To find B we can use B =Y- A*X
      • B= 100000 ppm – 6250*20=25000
        Note: If you take the maximum ppm value for Y, you need to take the maximum mA current for X.
        You can also do vice versa, were you take minimum ppm and mA values.
        Remember that either of the above conditions (min or max) will not effect the final output value.
  • After calculation, we obtain these below equation:
    • CO2 : [ppm] = 6250*[mA]-25000

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