The reading on my FINCH doesn’t match the 4-20mA reading on my 3rd Party equipment

Overview

If your FINCH system and third-party equipment (such as a control system or display system) are displaying different volume readings, the issue often arises from differences in calibration or signal interpretation settings between the devices. The TD100 T22 4-20 mA output provides a linear signal between 4 mA and 20 mA points based on the levels set in the strapping chart. If this linear output is not calibrated or matched properly in the third-party device, inconsistencies in volume readings may occur.

This article will guide you through steps to resolve mismatches between your FINCH and other equipment.

Common Causes:

1. Calibration and Signal Interpretation Differences:
   1. The TD100 T22 and third-party devices may have different calibration points or strapping charts, leading to mismatched volume interpretations of the 4-20 mA signal.
   2. The 4-20 mA output from the TD100 T22 is a linear signal, typically spanning from the 4 mA point for an empty tank to the 20 mA point for a full tank, as defined in the strapping chart programmed into the TD100. If the third-party device doesn’t match this linear interpretation or is not configured with a strapping chart, it may not accurately represent the volume.
2. SPILL Alarm Behavior:
3. 1. The TD100 T22 caps the 4-20 mA signal once the SPILL alarm level is reached if the SPILL alarm level is set somewhere below the 20 mA point. If the third-party device does not account for this cap, the volume may be interpreted as lower than it actually is.

Resolving the Issue:

1. Verify Calibration and Signal Interpretation on Both Devices
   1. Check the TD100 T22 Settings:
      1. Connect the TD100 T22 to your computer and open the SensorLink software.
      2. In the ‘Set 4-20 mA Points’ section, review where the 4 mA and 20 mA points are set.
      3. Confirm that these settings reflect the correct volume levels for an empty and full tank.
   2. Calibrate the Third-Party Device:
      1. Access the third-party device’s calibration settings and ensure it uses the same 4-20 mA range (the same 4 mA and 20 mA points).
      2. If possible, import or set a strapping chart in the third-party device to match the TD100’s levels for accurate signal interpretation.
      3. Ensure that the third-party device recognizes that the signal is linear. If the third-party device does not have a strapping chart programmed into it, it may not provide an accurate reading.
2. Check for SPILL Alarm Threshold
   1. The TD100 T22 may limit the 4-20 mA signal when the liquid level reaches the SPILL alarm level, if this level is set below the 20 mA point, even as the tank continues to fill.
   2. If possible, configure an alarm or notification in the third-party device, indicating that the level has reached the SPILL threshold. This setting helps the device recognize that readings beyond the SPILL level are not available.
3. Test the System
   1. By testing at different points on the probe, or adjusting the liquid level in the tank, observe the readings on both the FINCH and the third-party device.
   2. If the volume readings are now aligned, the system has been accurately calibrated. If discrepancies continue, review each device’s configuration to confirm accuracy.