Capacitive Technology


Capacitive TechnologyMichell Instruments % RH sensors feature a capacitive thin-film polymer sensor. These sensors provide a high accuracy, excellent long-term stability and negligible hysterisis. They are insensitive to contamination by particulate matter, are not permanently damaged by liquids, and are resistant to most chemicals.

OPERATING PRINCIPLE

A capacitive humidity sensor works like a plate capacitor. The lower electrode is deposited on a carrier substrate, often a ceramic material. A thin polymer hygroscopic layer acts as the dielectric, and on top of this is the upper plate, which acts as the second electrode but which also allows water vapour to pass through it, into the polymer. The water vapour molecules enter or leave the hygroscopic polymer until the water vapour content is in equilibrium with the ambient air or gas. The dielectric strength of the polymer is proportional to the water vapour content. In turn the dielectric strength affects the capacitance, which is measured and processed to give a relative humidity measurement. By also measuring temperature a dew point or absolute humidity value can also be obtained.
 
PCMini52 PCMini52
Relative humidity and temperature transmitter mini probe..
PCMini70 PCMini70
Relative humidity and temperature mini probe...
PC33, 52 & 62 PC33, 52 & 62
Relative humidity and temperature transmitter analogue and digital...
PFMini72 PFMini72
Relative humidity and temperature transmitter...
PF211 PF211
Relative humidity and temperature transmitter...
SF52 SF52
Dew-point transmitter...
RM33 & 52 RM33 & 52
Relative humidity and temperature transmitter, HVAC room mount...
WM33 & 52 WM33 & 52
Relative humidity and temperature transmitter, multi unit...
WM261 WM261
Relative humidity transmitter...
WM281 WM281
Digital relative humidity/temperature transmitter for wall mounting...
WM291 WM291
Relative humidity/temperature digital transmitter for wall mounting...
DT262 DT262
Relative humidity transmitter...
DT269 DT269
Relative humidity transmitter...
DT282 DT282
Digital relative humidity and temperature transmitter for duct installation...
DT284 DT284
Digital relative humidity and temperature transmitter remote version...
DT722 DT722
Rugged industrial relative humidity and temperature transmitter...
 
WR283 WR283
Digital relative humidity and temperature transmitter remote version for high temperatures...
WR285 WR285
Digital relative humidity transmitter with remote probe for pressurised locals...
WR293 WR293
Digital relative humidity and temperature transmitter remote version...
WR295 WR295
Digital relative humidity and temperature transmitter for applications at pressures up to 30 bar (3MPa)...
H5000 & 5100 H5000 & 5100
Relative humidity sensor...
H3000 H3000
Capacitive humidity sensor...
H6000 & 6100 H6000 & 6100
Relative humidity sensor...
I7000 & 7400 (Hygrosmart) I7000 & 7400 (Hygrosmart)
Interchangeable sensor module for relative humidity...
DM509 & 535 DM509 & 535
Hand-held relative humidity and temperature transmitters...
S503 S503
Humidity calibrator...
S904 S904
Relative humidity and temperature calibrator...
SCI SCI
Sensor communication interface...