What Is a Humidity and Temperature Transmitter? Types and Selection Criteria
A humidity and temperature transmitter measures the relative humidity and temperature of a space and converts them into an analog signal that a PLC, indicator or controller can read.
A humidity and temperature transmitter is a measuring device that measures the relative humidity and temperature of a space and converts these values into an analog signal that a PLC, indicator or controller can read. It is used to monitor conditions in ventilation ducts, greenhouses, warehouses, incubators and drying systems. A transmitter does not switch a load: to run a humidifier or heater, a humidity and temperature controller or a PLC reads the signal.
Types
- Wall type (Enda ESHT102-W-50): Measures the ambient air of a space such as a room, warehouse or greenhouse.
- Duct type (Enda ESHT102-DC-350): Mounted on a ventilation duct; the probe sits in the air flow inside the duct.
- Cable type (Enda ESHT102-CB-350): The sensor is at the end of a cable; the measuring point is in places such as a cabinet, incubator or drying room where the electronics housing must stay outside.
- Temperature-only transmitter (Isıso D148, D149): Converts a PT100 or thermocouple signal to 4–20 mA; it does not measure humidity. The D148 fits inside the probe's connection head and the D149 on a DIN rail.
- Device-specific sensors (GEMO GM-HT-01, Tense NT-310): Made as the sensor for specific controllers; verify the compatible device from the manufacturer data.
Catalog transmitters compared
| Model | Measures | Mounting | Output |
|---|---|---|---|
| Enda ESHT102-W-50 | Relative humidity + temperature | Wall | 0–20 mA or 0–10 V, selected on the device |
| Enda ESHT102-DC-350 | Relative humidity + temperature | Duct | 0–20 mA or 0–10 V, selected on the device |
| Enda ESHT102-CB-350 | Relative humidity + temperature | Cable | 0–20 mA or 0–10 V, selected on the device |
| Isıso D148 | Temperature (PT100 / thermocouple input) | Inside connection head | 4–20 mA |
| Isıso D149 | Temperature (PT100 / thermocouple input) | DIN rail | 4–20 mA |
The ESHT102 supply in the product data is 15–35 V DC or 10–25 V AC. The programming cable used to configure the D148 (D148 CABLE) is sold separately.
Selection criteria
- Quantity to measure: ESHT102 if you need humidity and temperature together; Isıso D148 or D149 if you only measure temperature and have a PT100 or thermocouple probe on site.
- Mounting location: Wall type for ambient air, duct type for duct air, cable type for tight or hot spaces.
- Output signal and reader input: Check whether the reading device expects current or voltage. The Enda EHTC7425A-AS has 0–20 mA and 0–10 V inputs and provides a 15 V DC (50 mA) sensor supply; this is at the bottom of the ESHT102's 15–35 V DC range, so compare the transmitter's consumption in the datasheet or use a separate supply.
- Supply: The ESHT102 runs on 15–35 V DC or 10–25 V AC; it is not connected directly to 230 V mains.
- Measuring point: Next to a sunlit wall, heater, door or humidifier outlet the sensor does not represent the space. In a duct, place the probe where the air flow is well mixed.
Common mistakes
- Confusing 0–20 mA with 4–20 mA: At 0–20 mA, 0 mA can mean either the bottom of the range or a broken cable; at 4–20 mA anything below 4 mA indicates a fault. The range on the reading device must be set the same as the transmitter.
- Not matching the scaling: If the transmitter's 0–100 % RH range is scaled differently on the indicator, the reading is wrong.
- Expecting humidity from an Isıso transmitter: The D148 and D149 only convert a temperature signal.
- Trying to drive a load with a transmitter: The output is a measurement signal; it cannot drive a relay or contactor.
Brands in the catalog
The Humidity and Temperature Transmitters category has 8 active products: Enda 3 (ESHT102 wall, duct and cable types), Isıso 3 (D148, D149 and the D148 programming cable), GEMO 1 (GM-HT-01), Tense 1 (NT-310). Probes for the D148 are in the Head Type Temperature Probes category, and devices to display a 4–20 mA signal are in Process Indicators.
Frequently asked questions
What output signal does a humidity and temperature transmitter give?
The Enda ESHT102 in the catalog gives a 0–20 mA or 0–10 V output selected on the device. The Isıso D148 and D149 temperature transmitters have a 4–20 mA output.
Should I choose a wall type or a duct type?
Choose a wall type to measure the air of a room or warehouse and a duct type to measure the air in a ventilation duct. If the measuring point is too tight or too hot for the device housing, use the cable type.
Can a transmitter run a humidifier on its own?
No. A transmitter only gives a measurement signal. To switch on a humidifier or heater you need a controller or PLC that reads the signal and switches a relay output.
What is the difference between the Isıso D148 and D149?
Both convert a temperature signal to 4–20 mA. The D148 fits inside the probe's connection head and converts the signal to current right at the probe; the D149 mounts on a DIN rail inside the panel.