The HU-227 Outside Air Humidity and Temperature Sensor is designed to handle 100% condensing humidity. The electronics are moisture sealed with an acrylic coating, and the sensing element is protected with an ePTFE (expanded Teflon) filter media. The unit can be directly mounted inside fresh air hoods of air handlers or underneath roof overhangs of any building. The sensor can also be installed inside the air handler fresh air duct.
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. The rugged NEMA-4 (IP-65) rated steel enclosure, thick-walled aluminum probe and gasket sealed cover offer a reliable solution for factory-mounted applications.
Each HU-227 is calibrated at multiple points in a NIST traceable calibration chamber to meet or exceed ±2% RH or ±3% RH accuracy. Units are temperature compensated over -30°F (-35°C) to +130°F (55°C) temperature range operation with negligible error. HU-227 is available with more than 16 types of interchangeable NTC thermistors, precision platinum, nickel or balco RTDs for universal compatibility.
The HU-227 incorporates a cross-linked bulk polymer capacitive humidity sensor and precision
NTC thermistor, platinum or balco RTD temperature sensor. Both temperature and humidity sensors are immune to most contaminants and at the same time provide a stable, repeatable, accurate humidity and temperature
measurement with negligible hysteresis. The sensing elements are not affected by condensation.
In fact, the probe may be immersed in distilled water without degrading the calibration
accuracy. The HU-227 utilizes sophisticated integrated circuits to provide a high level, fully conditioned, and temperature compensated humidity output. The thermistor temperature sensors are available with more than 16 different industry standard resistance to temperature
curves offering compatibility to most if not all
control systems. All thermistor sensors offer
±0.2°C interchangeability/accuracy and strictly
conform to industry standard R/T curves. The
platinum RTD’s are available with 100 ohm or
1000 ohm DIN 43760 standards with ±0.12%
accuracy at 0°C. All temperature sensors have
more than 3.0 mW/°C heat dissipation
On VDC output units (humidity only), 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. 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 (humidity only) 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
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 a 1500 ohm
load. In this way, the output loop can be tied in
series to multiple controllers, indicators, and
other devices without degrading the
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.
The PCB electronics are coated and sealed with
an acrylic conformal coating to protect against
moisture, condensation and contaminants.
The HU-227 incorporates a rugged NEMA-4
(IP-65) fully gasketed, dust proof and splash
proof enclosure. The enclosure has an external
mounting bracket to facilitate field installation. A
½” (.875”/22.25 mm diameter) knock-out for
conduit connection is also provided. A liquid
tight cable connector is supplied if the unit is not
being hard wired. Once installed, the enclosure
maintains its environmental rating and protects
the electronics and the sensing element from
condensation, corrosive contaminants and other
environmental pollutants. The enclosure also
has additional features for ease of installation
including unpluggable terminal block and easily
accessible zero and span trimmers.