Convert Millivolt Signals to Noise Immune 4-20mA at the Sensor Head

Temperature transmitter solutions for demanding industrial applications. The DR4401 4-20mA Temperature Transmitter series delivers reliable performance.

How We Solved EMI-Induced Thermocouple Drift in a Distillation Column

At the Johnson Chemicals plant in Q4 2021, erratic temperature readings from thermocouples in the distillation column caused over $50,000 in lost production and reprocessing. The root cause? Electromagnetic interference (EMI) from nearby variable frequency drives (VFDs) corrupting the millivolt-level signals.

The Physics Behind the Problem
Thermocouples generate a small voltage (millivolts) proportional to temperature. This low-level signal is highly susceptible to EMI from motors and VFDs, which induce noise that can cause fluctuations of ±5% or more. Simply moving the sensor away didn’t help because the interference was still coupled into the signal wires.
The Solution: Convert to 4-20mA at the Sensor Head
We switched to the DR4401 temperature transmitter, which converts the thermocouple signal to a robust 4-20mA output. Current loops are far less affected by EMI because the signal is transmitted as a current rather than a voltage, making it immune to voltage drops and induced noise. The DR4401 accepts RTD or thermocouple input, is configurable via software or DIP switches, and includes sensor break detection for failsafe operation. It offers DIN rail or head mount options, high accuracy and stability, and a 4-20mA output.
Results
After installation, temperature jitter dropped from ±5% to ±0.1%, false alarms ceased, and plant reliability improved. The DR4401 thermocouple transmitter proved to be a cost-effective fix for a pervasive industrial problem.
Is your process plagued by erratic temperature readings from EMI? The DR4401 could be your solution. Download the datasheet to see full specifications.

Tags: #temperaturetransmitter #RTDtransmitter #thermocoupletransmitter #4-20mAoutput #DR4401