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HU-224/225 Humidity Transducer


The HU-224/225 is an extremely fast, stable and accurate humidity transducer designed for harsh environments. The polymer capacitance sensor is protected with an ePTFE (expanded Teflon) filter media. The Teflon protected cross-linked capacitive humidity sensor is not affected by prolonged exposure to condensing humidity, harsh environments, contaminants, fog or other extreme environmental conditions. Each unit is individually calibrated in an environmental test chamber to meet or exceed NIST traceable ±2% or ±3% accuracies. The HU-224/225 is temperature compensated for -30°F (-35°C) to -130°F (55°C) operation with negligible error. For space humidity, an aesthetically appealing ABS enclosure which may be flush mounted or fits a standard 2" x 4" handy box is available, and for duct humidity applications, a rugged NEMA-4 (IP-65) steel enclosure with external mounting bracket is also available. Two enclosure types, field selectable outputs, fully temperature compensated NIST traceable accuracy, non-interacting zero and span adjustments, short circuit and reverse polarity protected output, and a liberal five year warranty are some of the features which make the HU-224/225 the industry's highest performance, most reliable humidity sensor.

The HU-224/225 incorporates a cross-linked bulk polymer capacitive humidity sensor which is immune to most contaminants and at the same time provides a stable, repeatable, accurate humidity measurement with negligible hysteresis. The sensing element is not affected by condensation. In fact, the probe may be immersed in distilled water without degrading the calibration accuracy. The HU-224/225 utilizes sophisticated integrated circuits to provide a high level, fully conditioned, and temperature compensated humidity output.

On VDC output units two additional field selectable options are available; dual outputs 0-5 or 0-10 VDC, and dual unregulated supply voltages 12-35 VAC or 12-40 VDC. By merely moving a switch, one can select the desired output for the specific application. As far as supply voltage is concerned, the unit automatically configures for AC or DC and no field selection is necessary. Another feature is that the output is fully protected from short circuit to ground, or if the supply voltage is applied by mistake to the output. Past experience demonstrates that field related wiring problems do occur. Instead of denying this fact, this protection circuit is designed in to ensure trouble-free start-up. The VDC output unit is also designed to handle low impedance circuits. In fact, the unit can drive up to 1K ohm minimum. In this way, multiple controllers, indicators, or other devices can be paralleled to the output without performance degradation.

The mA output units can function over a wide unregulated supply voltage range: 12-40 VDC without any effect on calibration or performance. The unit has reverse polarity protection built in. As a result, it is next to impossible to damage the unit by wiring incorrectly. By using sophisticated low dropout voltage regulators and CMOS integrated circuits, the mA output unit can drive very high output impedance. In fact, with only 12 VDC supply, the unit can drive 250 ohms. At 40 VDC, the unit is capable of handling up to 1500 ohms load. In this way, the output loop can be tied in series to multiple controllers, indicators, and other devices without degrading the performance.

The humidity sensor is protected by an ePTFE (expanded Teflon) filter media that incorporates a proprietary process of expanding or stretching an ultra thin Teflon sheet during the manufacturing process to create less than 1.0 micron (0.000039 inch) pores or holes. The hydrophobic and oleophobic characteristics of Teflon force moisture, condensation and other contaminants to form a bubble larger than the pore size, and the surface tension of the Teflon stops the water or other contaminants from passing through the filter media, thereby protecting the sensing element. However, air with absorbed moisture can easily penetrate the filter media. NIST traceable humidity standards are utilized to calibrate and certify the HU-224/225. Calibration data on each unit is archived digitally for SPC and QC purposes. All automated calibration systems are networked and data is available online to numerous individuals at the same time. In this way, extremely high standards of quality and calibration integrity are maintained.

The HU-224/225 incorporates a rugged NEMA 4 (IP-65) fully gasketed, dust proof and splash proof enclosure for monitoring duct humidity or an aesthetically appealing ABS plastic wall mount enclosure for monitoring space humidity. The HU-224 duct enclosure has an external mounting bracket to facilitate field installation. A ½" (.875"/22.25mm diameter) knock-out for conduit connection is also provided. A liquid tight cable connector is also supplied if the unit is not being hard wired. The HU-225 wall mount enclosure may be flush mounted on any flat surface or fits a standard 2" x 4" handy box. Louvers are provided on the top and bottom of the enclosure to ensure ample air flow for fast response. Both enclosure options also have additional features for ease of installation including unpluggable terminal block, easily accessible zero and span trimmers, and conveniently located switches for field selection.