What products are involved in this article?This article is based on the use of the SME (Smart Module Electronics) from SRV, SRD, DVP and DVM, using its 4-20mA ports. Hence it can be used for any of these Rheonics sensors.
What is the purpose of this article?Indicate frequent problems and possible solutions, that the user can encounter when trying to read signals through the 4-20mA channels from the SME.
| Issue | Possible Solution |
| Electronics | |
| No LED lights, display, or output signals are shown in the SME-TRD display. | Check the power supply and cabling. |
| Probe | |
| Wrong or no values are shown on the RCP. | Verify correct cabling from sensor to SME. https://support.rheonics.com/en/support/solutions/articles/81000297454-connecting-sensor-cable-colored-wires-to-transmitter-electronics |
| Check for error texts on the RCP. https://support.rheonics.com/en/support/solutions/articles/81000393091-sensor-error-status-and-parameter-status | |
| Communication | |
| Analog Signals output is 0mA | Check correct values on RCP |
| Check wires between SME and Analog reader. | |
| Ensure that 4-20mA communication was enabled before ordering. | |
| Verify 4-20mA settings in the service tab on RCP. | |
| Analog signals are less than 2mA | The power supply is lower than the minimum required for the SME. |
| Data reading | |
| Not enough decimal points in my readings. | Verify the resolution from the analog reader and scale range of the analog output. |
| 4-20mA can´t ensure the same amount of decimal points such other communication protocols. | |
| The measured viscosity value is different from my reference standards. | Viscosity values from Rheonics Sensors should not be expected to match laboratory instruments. |
| The measured temperature value is different from my reference standards. | Temperature is measured with an internal PT1000, check resistance values with the Sensor Diagnostic Sheet. |
| The values read are very oscillating and not stable. | Ensure the analog cable from the SME to the analog reader is shielded, especially if the environment has mechanical or electrical noise. Check article: https://support.rheonics.com/en/support/solutions/articles/81000408323-best-practices-for-cabling-installation |
| Readings are increasing with time. | Verify that the same behavior is shown in the RCP to discard problems with analog signal cables. |
| Check if deposits are formed around the sensor probe in line. | |
| Values don't go higher than a fixed value. | Check 4-20mA settings on RCP, and verify maximum value. |
| Analog signals differ from those read by the analog reader and those shown on the RCP. | Verify that the 4-20mA range set on the RCP is the same as the analog reader. Do a calibration check for the SME analog outputs on the RCP |
Resources:
1. What can go wrong with 4 - 20mA loops?
3. How to diagnose and fix your 4-20mA channel output data inconsistency?