Humidity Instruments
HygroSmart WM Series
Advanced Wall Mount Relative Humidity & Temperature Transmitters
The WM Series advanced wall mount transmitters are designed to reliably and accurately
measure moisture and temperature in a wide variety of industrial and process applications.
These rugged and fl exible transmitters feature the new generation HygroSmart I7000XP
interchangeable sensor — minimizing downtime and reducing maintenance costs.
WM291
HS
Highlights
• Accuracy ±1.25% RH
• Calculated hygrometric outputs
• Flexible analog output confi gurations
• Interchangeable sensor for rapid maintenance
• Digital RS485 Modbus multidrop output
• Optional integral LCD display
• Rugged heavy industrial housing
• Customer confi guration software for fl exibility
• Traceable 5-point calibration certifi cate
• Operating temperature –40 to +85°C
(–40 to +185°F)
WM281
HS
Applications
• Food processing
• Pharmaceutical
• Environmental
• Meterological
• Agricultural
• Power
• Energy
• Nuclear
• Paper processing
• Transportation
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Humidity Instruments
HygroSmart WM281 & WM291
The Adaptable Transmitter
Process control customers need to have reliable and stable
instrumentation giving repeatable data to the control system
to minimize downtime, ensuring long-term process accuracy.
The HygroSmart WM281/291 advanced wall mount relative
humidity and temperature transmitter allows fl exible on-site
reconfi guration with user-friendly software.
It uses the latest Michell advanced H8000 capacitive polymer
element, developed over 40 years of specialization in
challenging moisture measurements and now incorporated
into the new I7000XP (extra performance) interchangeable
sensor, within the transmitter.
Flexible Customer Outputs
The HygroSmart WM Series has a choice of many analog and
digital outputs, ensuring it is compatible with a variety of data
aquisition systems.
• 4–20 mA / 0–20 mA
• 0–1, 5, 10 V
• RS485 Modbus RTU output
• Outputs are confi gurable at ordering or on site
• Confi guration is achieved via the display or the Digicor2
software communication kit
Measurement Performance
The new H8000 capacitive polymer element and high
resolution electronic hybrid within the interchangeable sensor,
gives the new HygroSmart WM281/291 outstanding accuracy
across the complete RH and temperature spectrum.
• WM281/291 system accuracy ±1.25% RH
• ±1% RH long-term stability per year
Integral Display
The optional display and keypad of the advanced transmitter
allows for quick readings of data as well as easy on-site
reconfi guration of measured parameters.
Ease of Maintenance
The WM281/291 transmitters feature an interchangeable
sensor, which holds its own calibration data, giving a 30
HS
second maintenance time to replace the measurement
sensor, minimizing system downtime.
• No on-site calibration required
• Economical cost for the interchangeable sensor
• Minimizes downtime
User Flexibility
The WM281/291 transmitters have an RS485 Modbus
RTU digital interface, which can be used for either digital
multidrop outputting or for transmitter reconfi guration.
• Reconfi guration of analog mA, voltage outputs
• Reconfi guration of third calculated hygrometric output
• Adjustment of the display settings
Reliability of Supply
The transmitters are manufactured within Michell’s highvolume manufacturing facility, which ensures a reliable ontime delivery.
• Field supported by a network of Michell’s global service
centers
• Calibration manufacturing system is traceable to national
standards
System Customization
If your application requires a customized sensor solution, we
have a specialized design and manufacturing capability to
cover your requirements.
Measurement Operating Envelope
The new HygroSmart WM281/291 transmitters operate to the
defi ned technical specifi cations within the following operating
condition envelope:
RH%
100
75
50
Maximum mixing ratio
250g water/kg dry air
25
-40 0 5025 70 85
Temp °C
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Process Instruments
Technical Specifi cations
Product WM281-XP WM291-XP Display
Performance Specifi cations
RH measurement range 0 to 100% RH
RH accuracy @ 23°C (73°F) ±1.25% RH (5 to 95% RH)
RH thermal coeffi cient <0.03% RH/°C typical
RH measurement response time Less than 10 seconds
RH element Michell H8000
RH long term stability ±1% RH per year
Temperature measurement range –40 to +85°C
Temperature accuracy ±0.2°C
Temperature analog output accuracy ±0.2°C pro-rata per 100°C output signal span
Temperature resolution 0.01°C
Temperature technology PT100 1/3 DIN
Recommended storage range +10 to +40°C (+50 to +104°F)
Calibration Traceable 5-point calibration certifi cate
Electrical Specifi cations
Output signals 0–1 V, 0–5 V, 0–10 V, 4–20 mA, 0–20 mA
Digital output signal Modbus RTU over RS485 2 wire
mA load resistance Max 500 Ω over voltage supply range
Supply voltage range 15 to 21 V AC or 18 to 30 V DC
Power consumption 1.7 W max
Dew point:
Calculated 3rd output scales/range
CE conformity 2004/108/EC, 94/9/E
Communication kit (optional) Digicor2 280/290 software, USB to RS485 interface cable
Mixing ratio:
Absolute humidity:
Specifi c enthalpy:
Frost point:
Display Specifi cations
Display type LCD, 2 lines x 16 characters
Display confi guration Digicor2 communication kit and display keypad
Display confi guration variables
Display confi guration output variables
Operating Specifi cations
Operating temperature
Probe:
Housing:
Storage:
Mechanical Specifi cations
Ingress protection IP65 (NEMA 4 level)
Probe:
Housing:
Material
Dimensions
Weight 450g (1lbs) approx
Electrical connections Internal screw terminals
Filter assembly:
Probe:
Housing:
–40 to +100°C (–40 to +212°F)
0 to 500 g/kg
0 to 600 g/m
0 to 1500 KJ/kg
–50 to +10°C (–58 to +50°F)
Contrast, temperature averaging, RH averaging, temperature
Output RH signal, output temperature signal, calculated 3rd
–40 to +85°C (–40 to +185°F)
–30 to +70°C (–22 to +158°F)
–40 to +70°C (–40 to +158°F)
Delrin
Aluminum die casting
Stainless steel sintered fi lter
Stainless steel sintered fi lter with Tefl on
Slotted Delrin cap with stainless steel mesh filter
Slotted Delrin cap with PTFE filter
L=100mm (3.9”), ø19mm (ø0.7”)
120 x 120 x 49.5mm (4.7 x 4.7 x 1.9”)
3
(Digicor2-CK-01)
units
output, Modbus set-up
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Humidity Instruments
Product Dimensions
WM281-XP WM291-XP
The orange HygroSmart symbol is used to identify any Michell RH product which has the latest generation HS3
HS
interchangeable sensor
The blue HygroSmart symbol identifi es products using the I7000XP generation interchangeable sensor
HS
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Michell Instruments, Inc 319 Newburyport Turnpike, Suite 207, Rowley, MA 01969
Tel: 978 484 0005, Fax: 978 843 7669, Email: us.info@michell.com, Web:
Michell Instruments adopts a continuous development programme which sometimes necessitates specifi cation changes without notice.
Issue no: WM281 291_97185_V2_US_0216
www.michell.com/us
© 2016 Michell Instruments
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