Vaisala HMW90 High-Accuracy Humidity and Temperature Transmitter

Vaisala HMW90 Humidity and Temperature Transmitter

The wall-mounted Vaisala HMW90 Series provides high-accuracy humidity and temperature measurement for demanding HVAC, data-centre, laboratory, museum and warehouse environments.

  • Humidity accuracy up to ±1.7% RH
  • Analog or Modbus RTU output models
  • Optional visible display and configurable relay
  • Field-replaceable measurement module with calibration certificate

Vaisala HMW90 High-Accuracy Wall-Mounted Humidity and Temperature Transmitter

The Vaisala HMW90 Series consists of high-performance wall-mounted humidity and temperature transmitters for indoor HVAC and building-automation applications that require excellent accuracy, long-term stability and dependable operation.

With humidity accuracy up to ±1.7% RH, temperature accuracy of ±0.2 °C within the specified central range, analog and Modbus RTU output options, and an exchangeable measurement module, the HMW90 is well suited to data centres, laboratories, museums, archives, production facilities, warehouses and testing environments.

The product family includes humidity-and-temperature models, temperature-only models, visible-display versions and customised configurations. The correct model can therefore be selected according to the required output signal, display, relay and measured parameters.

Why Choose the Vaisala HMW90?

  • High Humidity Accuracy: Measures relative humidity with accuracy up to ±1.7% RH from 0–90% RH at +10 °C to +40 °C.
  • Accurate Temperature Measurement: Provides temperature accuracy of ±0.2 °C from +20 °C to +30 °C.
  • Full Humidity Range: Measures from 0–100% RH in non-condensing indoor environments.
  • Analog and Digital Options: Available with 4–20 mA, 0–5 V, 0–10 V or isolated RS-485 Modbus RTU outputs.
  • Calculated Humidity Parameters: Selected models can output dew point, mixing ratio, enthalpy, wet-bulb temperature, dew-point depression and absolute humidity.
  • Easy Field Configuration: Accessible DIP switches simplify output, scaling and communication setup.
  • Convenient Calibration: Supports one-point adjustment using trimmers and two-point calibration through the service port.
  • Replaceable Measurement Module: The HTM10SP module can be exchanged in the field to simplify maintenance and restore traceable measurement performance.
  • Traceable Calibration: Each transmitter is supplied with a traceable calibration certificate.

HMW90 Series Models

ModelMeasurementOutput and Features
HMW92 Relative humidity and temperature Two 4–20 mA current outputs; display hidden by the sliding cover
HMW92D Relative humidity and temperature Two 4–20 mA current outputs with visible display
HMW93 Relative humidity and temperature Two 0–5 V or 0–10 V outputs, relay and display hidden by the sliding cover
HMW93D Relative humidity and temperature Two 0–5 V or 0–10 V outputs, relay and visible display
HMW95 Relative humidity and temperature Isolated RS-485 Modbus RTU; display hidden by the sliding cover
HMW95D Relative humidity and temperature Isolated RS-485 Modbus RTU with visible display
HMW90 Relative humidity and temperature Factory-configurable analog or Modbus RTU model with selected parameter scaling
TMW92 Temperature only One 4–20 mA current output
TMW93 Temperature only One 0–5 V or 0–10 V output with relay
TMW90 Temperature only Factory-configurable analog-output model

Humidity Measurement Performance

SpecificationPerformance
Measurement Range 0–100% RH, non-condensing
Accuracy at +10 °C to +40 °C, 0–90% RH ±1.7% RH
Accuracy at +10 °C to +40 °C, 90–100% RH ±2.5% RH
Accuracy at -5 °C to +10 °C and +40 °C to +55 °C, 0–90% RH ±3% RH
Accuracy at -5 °C to +10 °C and +40 °C to +55 °C, 90–100% RH ±4% RH
Typical HVAC Stability ±0.5% RH per year
Humidity Sensor Vaisala HUMICAP 180R

Temperature Measurement Performance

SpecificationPerformance
Measurement Range -5 °C to +55 °C
Accuracy at +20 °C to +30 °C ±0.2 °C
Accuracy at +10 °C to +20 °C and +30 °C to +40 °C ±0.3 °C
Accuracy at -5 °C to +10 °C and +40 °C to +55 °C ±0.5 °C
Temperature Sensor Digital temperature sensor

Calculated Humidity Parameters

Depending on the selected HMW90 configuration, the transmitter can provide humidity values beyond relative humidity and temperature.

ParameterTypical Use
Dew Point Indicates the temperature at which condensation may begin
Mixing Ratio Represents the mass of water vapour relative to dry air
Enthalpy Supports HVAC energy and air-treatment calculations
Wet-Bulb Temperature Supports evaporative-cooling and psychrometric analysis
Dew-Point Depression Shows the difference between ambient temperature and dew point
Absolute Humidity Expresses the amount of water vapour per unit volume

Analog Output Specifications

Output VersionTechnical Details
Current Output Two loop-powered 4–20 mA outputs for HMW92 models
Current-Output Loop Resistance 0–600 Ω
Current-Output Supply 10–28 V DC at 0 Ω load; 20–28 V DC at 500 Ω load
Current-Channel Isolation 500 V DC between output channels
Voltage Output Two 0–5 V or 0–10 V outputs for HMW93 models
Voltage-Output Load Minimum 10 kΩ
Voltage-Model Supply 18–35 V DC or 24 V AC ±20%, 50/60 Hz
Relay One relay on voltage-output models, maximum 50 V DC or 50 V AC, 500 mA

Modbus RTU Specifications

FeatureSpecification
Digital Interface Isolated RS-485
Protocol Modbus RTU
Modbus Address Range 1–247
End-of-Line Termination 120 Ω termination enabled with a jumper
Supply Voltage 18–35 V DC or 24 V AC ±20%, 50/60 Hz
Galvanic Isolation 1.5 kV

HMW90 for Data Centres

The HMW90 is suitable for demanding data-centre room measurements where stable humidity and temperature information is required by the building-management or data-centre infrastructure-management system.

  • Data-Hall Monitoring: Measures representative room temperature and humidity conditions.
  • Hot-Aisle and Cold-Aisle Areas: Supports environmental monitoring when installed at a representative wall location.
  • Cooling Control: Provides accurate input for HVAC control and cooling-system optimisation.
  • Humidity Risk Management: Helps identify excessively dry or humid conditions around sensitive electronic equipment.
  • Modbus Integration: Allows multiple HMW95 transmitters to share an RS-485 network with the building-automation system.

For a broader overview, see our Vaisala Data Centre Environmental Monitoring Guide.

Common Applications

  • Data Centres: High-accuracy room humidity and temperature measurement.
  • Museums and Archives: Stable environmental monitoring for sensitive collections and documents.
  • Laboratories: Dependable monitoring of controlled indoor test and research environments.
  • Production Facilities: HVAC monitoring in industrial and controlled manufacturing areas.
  • Warehouses: Environmental measurement for humidity-sensitive materials and finished products.
  • Testing Facilities: Accurate room-condition measurement around test equipment and controlled spaces.
  • Premium Commercial Buildings: High-performance HVAC monitoring and building automation.

Installation Guidance

  • Install the transmitter where air circulates freely and represents the occupied or controlled space.
  • Avoid direct sunlight, exterior walls, heaters and equipment that generates local heat.
  • Do not place the sensor directly in supply-air discharge or close to doors that create rapid local changes.
  • Avoid mounting above equipment or cable openings that produce warm air currents.
  • Seal wall or conduit openings behind the mounting base to prevent false readings caused by air leakage.
  • Install the backplate and wiring during construction, then attach the electronics after dusty work is complete.

Calibration and Maintenance

The sliding enclosure cover provides access to the adjustment controls and service connection without removing the transmitter from the wall.

  • One-Point Adjustment: Offset trimmers allow convenient field adjustment on applicable models.
  • Two-Point Calibration: The service port supports calibration using a compatible computer connection or Vaisala handheld reference instrument.
  • Exchangeable Module: The HTM10SP humidity-and-temperature module can be replaced in the field.
  • Traceability: Replacement modules and transmitters are available with traceable calibration certificates.
  • Tamper-Resistant Option: Configurations without adjustment trimmers can be selected when adjustment should only be possible through the service port.

Operating and Mechanical Specifications

SpecificationValue
Operating Temperature -5 °C to +55 °C
Storage Temperature -30 °C to +60 °C
Maximum Wire Size 2 mm² or AWG 14
Service-Port Connector Four-pin M8
Approximate Cover Dimensions 132.7 × 81 × 30 mm
Colour Options Standard white or black for configurable HMW90 and TMW90 models

Related Vaisala HVAC Instruments

Selecting the Correct HMW90 Model

RequirementRecommended Model
4–20 mA humidity and temperature outputs HMW92 or HMW92D
0–5 V or 0–10 V outputs HMW93 or HMW93D
Relay with analog voltage outputs HMW93 or HMW93D
Modbus RTU communication HMW95 or HMW95D
Visible local display Select the D version of HMW92, HMW93 or HMW95
Temperature-only measurement TMW92, TMW93 or configurable TMW90
Special analog scaling or calculated parameter Factory-configured HMW90

Vaisala HMW90 Supplier in Malaysia

Seacom Process Instruments supplies and supports the Vaisala HMW90 Series humidity and temperature transmitters in Malaysia.

Our team can assist with model selection, output type, display option, calculated parameter, relay configuration, Modbus integration, installation location and calibration planning.

Contact Seacom with your required humidity and temperature range, output signal, building-automation interface and application conditions for a suitable HMW90 configuration.

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