When a humidity sensor is poorly matched to its installation, the failure is rarely dramatic. More often, readings drift in a hot process duct, a probe is exposed to pressure it was never designed for, or contaminants gradually degrade the sensing element until the data can no longer be trusted. Selecting the right version at the outset avoids all three. The A & B Series Digital Humidity & Temperature Sensors from Galltec+Mela, supplied and supported in the USA by Paquin, are built around that principle. They offer one measuring core in a range of configurations, from standard wall mounting to probes rated for -112 to 392°F (-80 to 200°C) or for pressures up to 25 bar (approx. 363 psi).
Two series built on one measuring core
Every version measures humidity with a capacitive thin-film Mela sensing element and temperature with a Pt1000 element. At 73.4°F (23°C), humidity is measured to within ±1.5% RH across the 10–90% RH span (±2% RH beyond it), and temperature to within ±0.36°F (±0.2°C). The two series differ in how the probe and transmitter are joined:
- A Series (exchangeable): a calibrated sensor part with a four-pin plug connects to a separate transmitter. Calibration values are stored in the sensor part, so probes and transmitters can be combined to suit the installation, and a probe can be exchanged without replacing the electronics.
- B Series (fixed): the sensor part and transmitter are permanently connected in a single assembly.
Matching the digital humidity and temperature sensor to the conditions
Both series are available in wall-mount, duct-mount and two-piece (remote probe) designs. Within those designs, special versions address particular operating conditions:
| Version | Probe operating range | Intended for |
|---|---|---|
| Standard | -40 to 185°F (-40 to 85°C) | General industrial air measurement |
| Duct, high temperature | -58 to 302°F (-50 to 150°C) | Hot air in ducts |
| Two-piece or thermally decoupled | -112 to 392°F (-80 to 200°C) | Very low or very high temperatures |
| Pressure-proof | -40 to 185°F or -58 to 302°F | Pressures from 20 mbar to 10 bar |
| HD (A Series sensor part) | -76 to 320°F (-60 to 160°C) | Ambient pressure up to 25 bar |
| Ammonia-resistant | -40 to 185°F or -58 to 302°F | Air containing ammonia |
| Vibration-protected sealing | -40 to 185°F | Installations subject to vibration |
The ratings apply to specific versions rather than to every sensor in the series. The transmitter electronics have their own ambient range of -40 to 185°F (-40 to 85°C), regardless of the probe. Apart from the pressure-proof and HD versions, the sensors are intended for unpressurized systems measuring non-aggressive air.
Interfaces and calculated values
Each sensor is ordered with an RS485 interface using the Modbus RTU protocol, for networks spanning up to 1,000 m, or an RS232 interface with an ASCII protocol, for runs up to 15 m. On Modbus versions, dew point, wet-bulb temperature, enthalpy, mixing ratio and absolute humidity are calculated within the sensor, based on normal atmospheric pressure, and these versions can be ordered with a display. The transmitter is rated IP65, and the A Series probe connector IP67.
Each Modbus sensor presents only 1/8 unit load, so up to 247 addressable sensors can share one bus. The datasheet's guidance for dependable networks is straightforward: daisy-chain the bus without spurs on screened, twisted-pair cable, terminate the first and last nodes, and keep the polling interval across the network at 2 seconds or less.
Filters, mounting and field verification
Protection of the measuring head depends on the filter selected. Duct and remote-probe designs ship with a sintered filter of stainless steel as standard (IP65), with PTFE-protected options that the manufacturer recommends for low air speeds, pollutant exposure or humidity persistently above 95% RH. Wall-mount versions offer protective baskets, membrane filters and sintered stainless steel filters. A range of accessories supports installation:
- Mounting plates for ducts and wall bushings, including a version for ammonia-containing gases
- Pressure-tight feed-through fittings rated to 6 bar at 180°C (brass) or 10 bar at 150°C (stainless steel)
- A weather protection housing recommended for outdoor installations
- Reference humidity standards (from 12% up to 97% RH) for checking accuracy on site
Placement matters as much as the sensor. Choose a spot that reflects typical conditions rather than one near a heat source, an entrance, an exterior wall or a sunlit surface, and loop the cables so that any water runs off. Condensation does not damage the sensor, but readings are unreliable until it dries. Oils, paint aerosols and solvent vapors should be avoided at the sensing element.
Key specifications (snapshot)
| Parameter | Value |
|---|---|
| Humidity range / accuracy | 0–100% RH / ±1.5% RH (10–90% RH at 23°C), ±2% RH otherwise |
| Temperature element / accuracy | Pt1000, 1/3 DIN class B / ±0.2 K at 23°C |
| Humidity response | t63 < 10 s at 2 m/s |
| Probe temperature range | From -40 to 85°C (standard) up to -80 to 200°C, by version |
| Pressure capability | Up to 10 bar (pressure-proof) or 25 bar (HD), by version |
| Designs | Wall mount, duct mount, two-piece remote probe |
| Interfaces | RS485 Modbus RTU (to 1,000 m) or RS232 ASCII (to 15 m) |
| Supply voltage | 5–30 VDC |
| Transmitter ambient / protection | -40 to 85°C / IP65 |
Order designations, dimensions, the Modbus register map and wiring diagrams are in the A & B Series datasheet (PDF).
Configuring your A or B Series sensor
Analog-output versions and other Galltec+Mela humidity and temperature sensors are listed in Paquin's industrial humidity and temperature collection.
Tell us where the measurement point is and what the air is like there. On the A & B Series product page, share the mounting location, temperature and pressure range, anything unusual in the air, and the interface your system uses. Paquin will identify the series, design, version and filter that fit, and quote the complete sensor.
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