[Core Summary]
The repeated exceeding of compressed air dew point limits is often not due to insufficient output of the dryer, but rather to incorrect selection or installation location of the measuring point, leading to a discrepancy between the readings and the actual operating conditions. The E+E Elektronik (E+E, Austria) EE355 OEM dew point transmitter has a measurement range of –60…+60 °C Td, with a typical accuracy of ≤±2 °C Td. It is made of stainless steel 1.4404, with a pressure resistance of 0…80 bar. It also provides dual outputs of 4–20 mA and Modbus RTU, making it suitable for direct embedding in compressed air pipelines or dryer outlets for continuous monitoring. When selecting, it is more cost-effective to lock in the measurement range, reference pressure, output protocol, and installation location at once, rather than blindly increasing the power of the dryer.
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Why does the dew point alarm always jump around the "critical value"
Common on-site phenomenon: The dew point value fluctuates slightly around the alarm threshold, and the dryer frequently loads but cannot be lowered. Most of these issues arise at the measurement end—sensors are installed at abrupt changes in pipe diameter, behind elbows, or downstream of valves, where airflow disturbances and localized fluid accumulation distort the readings. Alternatively, the measurement range may be selected too broadly, diluting the resolution in the low-humidity segment, and small drifts are amplified into alarms. Check the measurement point location and range first, and then discuss the dryer parameters.
Scope of application and accuracy boundaries of EE355
The dew point measurement range of EE355 is –60...+60 °C Td, with a typical accuracy of ≤±2 °C Td. This range covers the majority of drying targets for instrument air and oil-free compressed air (typically requiring a pressure dew point of –40 °C Td or lower). It is important to note that accuracy specifications are tied to reference conditions, and the sample is given based on normal temperature and pressure. In extremely low dew point or high flow rate conditions, a margin should be maintained, and compliance should not be determined solely based on the nominal reference value.
The impact of pressure on dew point readings
Dew point is divided into "atmospheric dew point" and "pressure dew point". In compressed air, the measured dew point is the pressure dew point, and as the pressure increases, the dew point temperature corresponding to the same water content decreases. The EE355, with a pressure resistance range of 0...80 bar, can directly measure in pressurized pipelines, eliminating the deviations caused by pressure reduction sampling. When making quality judgments, it is important to distinguish whether the standard refers to the pressure dew point or the atmospheric dew point, as the conversion between the two may result in a difference of more than ten degrees Celsius. Confusion can directly lead to false alarms or missed alarms.
How to choose between 4–20 mA and Modbus
EE355 offers both 4–20 mA (three-wire system, load resistance < 500 Ω) and Modbus RTU (up to 32 devices on one bus). For retrofit projects with fewer points and existing AI channels on the PLC, choosing 4–20 mA is more convenient. For new station buildings or when multiple measurement points need to be centralized on one bus, Modbus can reduce cables and terminals, and facilitate the integration of dryer inlets and outlets, gas storage tanks, and gas utilization terminals into a trend. Note that the Modbus version should set the address during power-off to avoid conflicts with the host computer's planning.
Three pitfalls of installation location
Firstly, avoid the turbulent flow zone within 10 times the pipe diameter downstream of the valve and elbow; secondly, prevent direct scouring by condensate water at the probe location, and install automatic drains if necessary; thirdly, the stainless steel housing is only IP65 rated for water spray protection, not immersion protection, so a protective sleeve should be used outdoors or in washing areas. When wiring the M12×1 five-pin plug, ensure that the shielding layer is grounded at one end, otherwise the 4–20 mA signal is prone to sawtooth drift due to interference from the frequency converter.
Put it into the dryer's interlock logic
Connect the 4–20 mA of EE355 to the dryer controller or dew point joint control module, which can automatically switch to energy-saving mode after the dew point reaches the standard, reducing unnecessary regeneration air consumption and heating. It is recommended to set a hysteresis zone for the joint control logic (e.g., start regeneration at –38 °C and stop at –42 °C) to avoid frequent switching near the threshold values. This type of closed-loop system, which "measures accurately and starts/stops as needed," is more energy-efficient than constant full-load operation.
[Parameter Table]
**Parameter Source Description**: The table above is extracted from the E+E Elektronik EE355 product catalog. The volume concentration (ppm) range sample is not provided in the captured fields. Please verify the label [ ], and confirm with the manufacturer or agent before incorporating it into the technical agreement.
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