If you work with HVAC, building automation, or environmental monitoring, chances are you’ve encountered legacy but reliable analog transmitters. One of those hard-working devices is the EE20-FT6B51 moisture and temperature transmitter, a duct-mount unit that provides dual 4–20 mA outputs for relative humidity and temperature. In this guide, we’ll unpack how the EE20-FT6B51 moisture and temperature transmitter is built, what its codes mean, how to wire it correctly, and where it still shines in modern projects.
Although the EE20 series is no longer front and center in the current E+E Elektronik catalog, many systems around the world still depend on the EE20-FT6B51 moisture and temperature transmitter. Understanding its specifications and behavior helps you maintain existing installations, design compatible replacements, and troubleshoot data in your BMS, PLC, or SCADA system.
This article pulls together manufacturer family documentation, practical wiring guidance, and engineering references to give you a single, practical resource on the EE20-FT6B51 moisture and temperature transmitter—from sensing elements and accuracy to compliance, accessories, and real-world applications.
What Is the EE20-FT6B51 Moisture and Temperature Transmitter?
At its core, the EE20-FT6B51 moisture and temperature transmitter is a duct-mount HVAC-class instrument that measures relative humidity (RH) and temperature and converts those readings into two separate 4–20 mA signals. One loop corresponds to humidity (0–100% RH), and the other loop corresponds to temperature (typically −20 to +80 °C). This makes the EE20-FT6B51 moisture and temperature transmitter a convenient, two-in-one sensor for building climate control and process ventilation.
The transmitter uses a capacitive humidity sensor combined with a platinum resistance temperature detector (Pt1000) in the probe tip. Inside the enclosure, conditioning electronics linearize and temperature-compensate the humidity reading before mapping both humidity and temperature to the 4–20 mA outputs. Because the EE20-FT6B51 moisture and temperature transmitter is duct-mounted with a 200 mm probe, it can sample the actual airstream inside supply or return ducts where control decisions are made.
Typical applications for the EE20-FT6B51 moisture and temperature transmitter include building HVAC systems, indoor swimming facilities, greenhouses, stables, storage rooms, and meteorological or environmental monitoring setups. Anywhere you need reliable analog RH and temperature signals from a duct, this transmitter can integrate cleanly with PLC, DCS, or BMS analog input modules.
Decoding the EE20-FT6B51 Moisture and Temperature Transmitter Model Code
The part number on the label of an EE20-FT6B51 moisture and temperature transmitter isn’t just a random string—it encodes important details about outputs, housing style, probe length, and filter type. The “FT6B51” segment follows the same coding logic used in the closely related EE21 family, which lets us interpret the structure of the EE20-FT6B51 moisture and temperature transmitter reliably.
In this code, the “FT” indicates that the device is a combined humidity and temperature transmitter. The “6” denotes 4–20 mA outputs, which is why the EE20-FT6B51 moisture and temperature transmitter provides two analog current loops rather than voltage outputs. The “B” indicates duct-mount housing, aligning with the physical design where the probe penetrates the duct wall. The “5” refers to a probe length of 200 mm, and the final “1” identifies the use of a membrane filter at the sensing head.
From a practical design perspective, this means the EE20-FT6B51 moisture and temperature transmitter is optimized for duct installation with adequate penetration into the airstream, 4–20 mA current loop compatibility, and a protective membrane filter that balances response time and protection against contaminants. Understanding this code helps you cross-reference similar variants, evaluate replacements, and select accessories that match the mechanical form factor.
Electrical Specifications and 4–20 mA Outputs of the EE20-FT6B51 Moisture and Temperature Transmitter
One of the main reasons engineers choose the EE20-FT6B51 moisture and temperature transmitter is its straightforward 4–20 mA interface. Each channel—humidity and temperature—uses its own 4–20 mA current loop, but both share a common supply terminal. In a typical installation, the EE20-FT6B51 moisture and temperature transmitter is powered by a SELV (Safety Extra-Low Voltage) DC supply, and each output loop terminates in an analog input on a PLC or BMS.
In standard configuration, 4–20 mA from the humidity loop corresponds to 0–100% RH, while 4–20 mA from the temperature loop corresponds to −20 to +80 °C. Converting the signal from the EE20-FT6B51 moisture and temperature transmitter into engineering units is straightforward. For humidity, %RH = (I_mA − 4) × (100 / 16). For temperature, T(°C) = −20 + (I_mA − 4) × (100 / 16). These linear mappings make it easy to scale readings in your PLC logic or SCADA graphics.
The supply voltage for an EE20-FT6B51 moisture and temperature transmitter typically falls between 20 and 35 V DC for standard loop burdens up to about 500 Ω. At lower supply voltages, the permissible loop resistance decreases, so checking the burden of your analog input cards and cable runs is essential. Respecting these limits ensures each loop of the EE20-FT6B51 moisture and temperature transmitter can drive a full 4–20 mA span without saturating or dropping out.
Wiring the EE20-FT6B51 Moisture and Temperature Transmitter in Duct Systems
Even the best sensor will fail to deliver reliable signals if it’s wired incorrectly. The EE20-FT6B51 moisture and temperature transmitter follows a simple but specific terminal layout similar to the EE21 FT6 variants. Typically, terminal 1 is the shared positive supply (V+), terminal 2 is the return for the humidity loop, and terminal 3 is the return for the temperature loop. When you wire the EE20-FT6B51 moisture and temperature transmitter, each loop forms a series path: supply → transmitter → analog input burden → supply return.
Because the EE20-FT6B51 moisture and temperature transmitter uses current loops, you must avoid accidentally connecting outputs in parallel or tying returns together in creative ways. Each 4–20 mA loop should be independent, with its own burden resistor or analog input channel. This isolation helps prevent cross-talk and ensures each channel from the EE20-FT6B51 moisture and temperature transmitter can be calibrated accurately.
For best EMI performance, use shielded twisted-pair cable and terminate the shield at the receiving device end (for example, at the PLC panel earth). Do not ground the shield at both ends; this helps protect the EE20-FT6B51 moisture and temperature transmitter from noise and avoids ground-loop currents. A clean wiring layout with clearly labeled loops makes future maintenance and troubleshooting much easier.
How the EE20-FT6B51 Moisture and Temperature Transmitter Measures Humidity
The heart of the EE20-FT6B51 moisture and temperature transmitter is a capacitive humidity sensor, belonging to the HC1000-class family. This polymer-based sensor changes its capacitance as relative humidity varies, and the transmitter’s internal electronics convert that behavior into a linear, temperature-compensated RH signal. Within the 0–100% RH range, the EE20-FT6B51 moisture and temperature transmitter can achieve a typical accuracy of about ±2% RH in the mid-range.
In addition to basic accuracy, hysteresis and long-term stability matter in real installations. The capacitive element used in the EE20-FT6B51 moisture and temperature transmitter is designed for low hysteresis over typical humidity cycles and exhibits drift on the order of about 1% RH per year under controlled conditions. This performance allows for practical calibration intervals and predictable behavior, which is important when the EE20-FT6B51 moisture and temperature transmitter is used in energy-critical control loops such as demand-controlled ventilation.
Response time is influenced not only by the core sensor but also by the filter and airflow around the probe. The membrane filter on the sensing head of the EE20-FT6B51 moisture and temperature transmitter protects the element from dust and droplets while still permitting reasonable response. However, if the probe is installed in a stagnant location, or if the filter becomes polluted, apparent response times will increase and readings from the EE20-FT6B51 moisture and temperature transmitter may lag behind real conditions.
Temperature Measurement Capabilities of the EE20-FT6B51 Moisture and Temperature Transmitter
The temperature channel of the EE20-FT6B51 moisture and temperature transmitter is based on a Pt1000 resistance thermometer that complies with widely used industrial standards. In the −20 to +80 °C range, the transmitter converts the RTD reading into a linear 4–20 mA signal. This makes the EE20-FT6B51 moisture and temperature transmitter suitable for most comfort-climate and light industrial ventilation applications where air temperatures remain within that envelope.
Accuracy for the temperature channel is typically around ±0.3 °C in the normal room-temperature band, with a slightly increasing error outside that range. This is more than sufficient for HVAC control strategies that use the EE20-FT6B51 moisture and temperature transmitter as a feedback device for heating, cooling, or mixed-air dampers. Because humidity compensation relies on accurate temperature information, proper installation of the EE20-FT6B51 moisture and temperature transmitter in the airstream is essential.
It’s important to distinguish between measurement range and housing operating limits. While the EE20-FT6B51 moisture and temperature transmitter measures up to around 80 °C in the air stream, the electronics enclosure itself is usually rated for a somewhat lower ambient. In most duct installations, the housing sits outside the hottest air, and only the probe is exposed to elevated temperatures. Ensuring the body of the EE20-FT6B51 moisture and temperature transmitter remains within safe ambient limits is critical to long-term reliability.
Mechanical Design, Housing, and Environmental Protection
Mechanically, the EE20-FT6B51 moisture and temperature transmitter uses a polycarbonate (PC) enclosure that typically meets IP65 / NEMA 4 protection levels when installed with the cable gland correctly tightened. This allows the EE20-FT6B51 moisture and temperature transmitter to operate in dusty mechanical rooms or humid plant spaces without exposing internal electronics to moisture. The duct-mount “B” housing includes a mounting plate that lets you adjust the penetration depth of the 200 mm probe.
The probe itself is usually around 12 mm in diameter, which is a common standard for compatible accessories like radiation shields and drip-water protectors. At the tip of the EE20-FT6B51 moisture and temperature transmitter probe is the sensing head with a membrane filter. This filter is field-replaceable and is central to protecting the humidity sensor from contamination, insects, and droplets. A clean filter helps the EE20-FT6B51 moisture and temperature transmitter maintain fast response times and stable readings.
From an environmental standpoint, the EE20-FT6B51 moisture and temperature transmitter is suitable for a wide range of air-handling tasks: greenhouses, storage rooms, barns, swimming halls, and general building HVAC. However, in extremely polluted or aggressive environments (such as industrial exhaust ducts), you may need additional protection or a transmitter family with special protective coatings. Installing the EE20-FT6B51 moisture and temperature transmitter in accordance with manufacturer family guidelines ensures its enclosure and probe survive long-term exposure.
Installing the EE20-FT6B51 Moisture and Temperature Transmitter in Real Ducts
Good measurements start with good placement. When installing an EE20-FT6B51 moisture and temperature transmitter, aim for a location where the air is well mixed—often several duct diameters downstream of bends, dampers, or coils. This helps ensure the EE20-FT6B51 moisture and temperature transmitter sees representative temperature and humidity, not stratified layers or recirculation pockets.
The included duct mounting hardware allows you to slide the probe to the desired penetration depth and lock it in place. In most cases, you want the sensing head of the EE20-FT6B51 moisture and temperature transmitter to sit somewhere near the center of the duct, especially in large ducts. If the probe is too close to the wall, boundary-layer effects can distort readings. Always ensure the EE20-FT6B51 moisture and temperature transmitter is oriented so that condensate cannot run directly into the enclosure.
In outdoor or solar-exposed applications, it is better to install the probe in a radiation shield rather than directly in the sun. While the EE20-FT6B51 moisture and temperature transmitter is mechanically robust, direct solar loading can cause artificial temperature readings and stress the enclosure. A radiation shield and drip protection accessory help the EE20-FT6B51 moisture and temperature transmitter deliver accurate data even in harsh weather.
Calibration, Compliance, and Maintenance of the EE20-FT6B51 Moisture and Temperature Transmitter
Because humidity sensors can drift over time, calibration practice is important when using an EE20-FT6B51 moisture and temperature transmitter in critical applications. E+E Elektronik supports calibration services traceable to international standards through accredited laboratories, and the transmitter family allows for two-point adjustment of humidity readings. Periodic calibration ensures the EE20-FT6B51 moisture and temperature transmitter continues to meet accuracy expectations after years in service.
On the compliance side, the EE2x family—including devices like the EE20-FT6B51 moisture and temperature transmitter—is designed to meet EMC standards such as EN 61326 for emissions and immunity. The company also provides RoHS and REACH declarations, ensuring that materials in the EE20-FT6B51 moisture and temperature transmitter follow current European environmental regulations. This is useful for specifiers working on projects that require formal documentation for audits or certifications.
Routine maintenance for an EE20-FT6B51 moisture and temperature transmitter usually centers on the filter and the mechanical installation. If readings become sluggish or humidity values seem unrealistically high, check for condensation or contamination. Dry the probe, replace the membrane filter if necessary, and verify that the EE20-FT6B51 moisture and temperature transmitter is not exposed to continuous drips or standing water. A simple inspection schedule can greatly extend sensor life.
Accessories and Alternative Solutions for the EE20-FT6B51 Moisture and Temperature Transmitter
In many installations, the performance of an EE20-FT6B51 moisture and temperature transmitter can be improved with the right accessories. Radiation shields, drip water protectors, and protective caps help shield the probe from rain, sunlight, and aggressive cleaning. When mounted outdoors or in areas with possible condensation, these accessories give the EE20-FT6B51 moisture and temperature transmitter a more controlled micro-environment and reduce the risk of liquid water on the sensing head.
For panel builders and installers, conduit adapters and DIN-rail brackets are also available. These make it easier to integrate the EE20-FT6B51 moisture and temperature transmitter into standard control panels and electrical infrastructures. Conduit fittings, for instance, help route cables to the housing cable gland while maintaining ingress protection, and a solid bracket prevents mechanical stress on the EE20-FT6B51 moisture and temperature transmitter enclosure.
Since the EE20 series is older, you may also need to consider replacements or functional alternatives in new projects. E+E Elektronik’s current catalog includes other HVAC-oriented humidity and temperature transmitters with 4–20 mA outputs that can substitute for an EE20-FT6B51 moisture and temperature transmitter. When selecting an alternative, match key parameters such as duct-mount geometry, dual current outputs, measurement ranges, and environmental ratings so that migration from an existing EE20-FT6B51 moisture and temperature transmitter is as seamless as possible.
Practical Use Cases for the EE20-FT6B51 Moisture and Temperature Transmitter
To appreciate the value of the EE20-FT6B51 moisture and temperature transmitter, it helps to look at real-world scenarios. In a building HVAC system, the transmitter might be installed in the supply air duct after a cooling coil. The humidity output from the EE20-FT6B51 moisture and temperature transmitter feeds a BMS that controls dehumidification, while the temperature output drives supply-air temperature reset logic. Both loops contribute to comfort and energy efficiency.
In a greenhouse, the EE20-FT6B51 moisture and temperature transmitter can monitor the growing environment in a duct providing conditioned air. The operator can use the humidity signal to manage misting or ventilation, while the temperature loop from the EE20-FT6B51 moisture and temperature transmitter helps maintain optimal plant temperatures. Because plants are sensitive to both temperature and humidity, pairing these two signals in one probe reduces wiring complexity.
In industrial or agricultural stables, where animals generate moisture and heat, a properly installed EE20-FT6B51 moisture and temperature transmitter helps keep conditions within healthy boundaries. Exhaust fans, louvers, and heaters can all be controlled from the RH and temperature loops. The robustness of the EE20-FT6B51 moisture and temperature transmitter and its protective filter make it a practical choice in moderately harsh atmospheres when installed correctly.
Troubleshooting Common Issues with the EE20-FT6B51 Moisture and Temperature Transmitter
Like any field device, the EE20-FT6B51 moisture and temperature transmitter can exhibit symptoms that signal installation or environmental problems. If humidity readings are persistently too high or stuck near saturation, check for condensation on the sensing head. Dry the probe, ensure the membrane filter is intact, and verify that the EE20-FT6B51 moisture and temperature transmitter is not installed where water can drip directly on the sensor.
If both channels read low or high simultaneously, consider wiring and power issues. Measure the loop current with a multimeter in series to confirm the EE20-FT6B51 moisture and temperature transmitter is actually sourcing a proper 4–20 mA signal. Incorrect burden resistances or analog input configuration can also lead to misinterpreted readings. Ensuring the analog cards are set for current mode and sized correctly is as important as choosing the right EE20-FT6B51 moisture and temperature transmitter.
Noise and instability in the signals may point to grounding and shielding problems. Check that cable shields are grounded only on the receiving side, and that the EE20-FT6B51 moisture and temperature transmitter is not sharing its supply with high-noise devices without proper filtering. A clean power supply and careful cable routing often stabilize readings from the EE20-FT6B51 moisture and temperature transmitter dramatically.
Related Product Collections for Your Next Project
Beyond the EE20-FT6B51 itself, you can simplify sourcing and ensure compatibility by exploring a few closely related product collections from Industrial Electrical Warehouse:
● Sensors ➜ – A broad range of industrial sensors, from proximity and photoelectric devices to process sensors, ideal for building out a complete sensing layer across your HVAC, BMS, or process automation system.
● Temperature Controllers ➜ – Digital and analog temperature controllers that pair well with 4–20 mA temperature outputs, helping you close the control loop for heating, cooling, and mixed-air strategies.
● Measuring Device ➜ – Measuring and test instruments that support commissioning, verification, and routine maintenance of humidity and temperature loops, including setups that rely on the EE20-series transmitters.
Exploring these collections alongside the EE20-FT6B51 moisture and temperature transmitter can streamline your next retrofit or new build and help ensure all components work together reliably.
Conclusion: Is the EE20-FT6B51 Moisture and Temperature Transmitter Right for Your Project?
The EE20-FT6B51 moisture and temperature transmitter remains a capable solution for duct-mount humidity and temperature measurement wherever dual 4–20 mA outputs are needed. Its capacitive RH sensor, Pt1000-based temperature channel, and robust IP65 housing make the EE20-FT6B51 moisture and temperature transmitter suitable for greenhouses, swimming halls, animal facilities, storage rooms, and a wide range of HVAC systems.
If you’re maintaining existing infrastructure, understanding the behavior, wiring, and accessories of the EE20-FT6B51 moisture and temperature transmitter will help you extend system life and plan sensible upgrades. For new builds, reviewing the specifications of the EE20-FT6B51 moisture and temperature transmitter alongside newer humidity/temperature transmitters can clarify whether this legacy design still aligns with your control strategy, environmental conditions, and compliance requirements.
When you’re ready to go deeper—comparing pricing, stock, and mechanical details—it’s helpful to review the dedicated product page for the EE20-FT6B51 moisture and temperature transmitter. There you can confirm part numbers, explore related accessories, and check potential alternatives so you can select the right sensing solution for your next HVAC or environmental monitoring project.
