Michell Instruments WM281 Specifications
Humidity and Dew-Point Instruments
Precision Manufacturing
WM281
Digital Relative Humidity & Temperature Transmitter, Wall Mount
Technical Specifi cations
Performance
Measurement range (RH) 0–100% RH
Measurement range (T) -30 to +70°C (-22 to +158°F)
HYGROSMART ®
INTERCHANGEABLE
MODULE
The WM281 relative humidity transmitter includes the
interchangeable Hygrosmart module. The interchangeable
module lets you recalibrate the transmitter simply by
replacing the sensor head with the Hygrosmart module. As a
result, maintenance costs are greatly reduced and down-time
is minimized.
Highlights
Analog and digital output standard•
Based on the interchangeable Hygrosmart module•
Analog output signals selectable through software•
Metric or US measurement units selectable through •
software
Accuracy at 23°C (73°F)
Humidity
Accuracy at 23°C (73°F)
Temperature
Stability – RH Sensor <±1% RH/year
Response time – RH Sensor <10 sec typical (for 90% of the step
Electrical output/input
Output signal confi gurable on
request
Supply voltage 15 - 27 V AC / 18 - 38 V DC
Load resistance Current output: R ≤ 500 Ω
Power consumption 1.7 W
Operating conditions
Operating temperature
Probe
Housing
Storage
Mechanical specifi cation
Ingress protection IP67
Material
Housing
Probe
Dimensions
Housing
Probe
Weight 450g (15.87oz)
Electrical connections Screw terminals
<±2% RH (5-95% RH)
±0.4°C (±0.72°F)
change)
0–1, 0–5, 0–10 V
0–20 mA, 4–20 mA, RS485
-30 to +85°C (-22 to +185°F)
-30 to +70°C (-22 to +158°F)
-40 to +70°C (-40 to +158°F)
Aluminum die casting
Delrin
120 x 120 x 49.5mm (4.72 x 4.72 x 1.94”)
L=100mm, ø 19mm (L=3.93”, ø0.74”)
Dimensions
Issue No: WM281_97185_V2_UK_1110
Accessories and Spare Parts
RS422/485 to PC (RS232) converter 330185
USB cable/software for confi guration F035263
SS sintered fi lter H2
SS sintered fi lter with tefl on coating J2
Delrin cap slotted with SS mesh fi lter K7
Delrin cap slotted with PTFE fi lter, white Z7
Hygrosmart with Pt100 output (RH = 0-1 V) I7-0-00-1
You can check your hygrometer with the Control Kit HKC
which is based on the principle of non-saturated salt
solutions. Refer to technical data sheet CONTROL KIT
41
Please note: Michell Instruments adopts a continuous development program which sometimes
necessitates specifi cation changes without notice. Please contact us for latest version.
HKC
www.michell.com
Humidity and Dew-Point Instruments
WM281
Electrical Connections
Pin Pin
1 Power Supply V + 8 Output Channel 2 Ground
2 Power Supply V - 9 RS485 Data +
3 Output RS485 Ground 10 RS485 Data -
4 Ground 11 Not connected
5 Output Channel 1 Temperature + 12 Not connected
6 Output Channel 1 Ground 13 Output Channel 3 (not connected)
7 Output Channel 2 RH + 14 Output Channel 3 Ground (not connected)
Do not connect pin 2 (V -) to pin 4 (Ground)
Ordering Codes
To construct the order code, select the relevant feature from the tables below, starting with the base model, which is {Feature A} and then add on options to create a
string: {Feature A}+{Feature B}+{Feature C}+{Feature D}+{Feature E}
Precision Manufacturing
Order example:
Digital RH and temperature transmitter WM281, 4-20 mA output, delrin cap slotted with stainless steel mesh fi lter, temp range -30 to +70ºC (-22 to +158°F)
Base Model {Feature A}
Digital RH and temperature transmitter WM281
Signal Output {Feature B}
4–20 mA A
0–10 V B
0–5 V C
0–1 V D
0-20 mA E
Filter {Feature C}
SS sintered fi lter H2
SS sintered fi lter with tefl on coating J2
Delrin cap slotted, with SS mesh fi lter K7
Delrin cap slotted, with PTFE fi lter,
white
WM281+A+K7+N030+P070
WM281 A K7 N030 P070
Temperature High {Feature E}
+20°C (+68°F) P020
+30°C (+86°F)) P030
+50°C (+122°F) P050
+70°C (+158°F) P070
Other output scaling available on
request
Temperature Low {Feature D}
0°C (+32°F) 0000
-20°C (-4°F) N020
-30°C (-22°F) N030
Z7
XXXX
© Michell Instruments 2009-2011
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