SHT1x / SHT7x Relative Humidity & Temperature Sensor System

www.sensirion.com

v2.02 July 2004

6/9

4 Applications Information

4.1 Operating and Storage Conditions

0

20

40

-40

0

100

40

80

120

60

80

100

[°C]

[%RH]

60

20

-20

Maximum operating

conditions

Normal operating

conditions

Figure 11 Recommended operating conditions

Conditions outside the recommended range may temporarily

offset the RH signal up to

±3 %RH. After return to normal

conditions it will slowly return towards calibration state by

itself. See 4.3 “Reconditioning Procedure” to accelerate this

process. Prolonged exposure to extreme conditions may

accelerate ageing.

4.2 Exposure to Chemicals

Chemical vapors may interfere with the polymer layers used

for capacitive humidity sensors. The diffusion of chemicals

into the polymer may cause a shift in both offset and

sensitivity. In a clean environment the contaminants will

slowly outgas. The reconditioning procedure described

below will accelerate this process. High levels of pollutants

may cause permanent damage to the sensing polymer.

4.3 Reconditioning Procedure

The following reconditioning procedure will bring the sensor

back to calibration state after exposure to extreme conditions

or chemical vapors.

4.4 Temperature Effects

The relative humidity of a gas strongly depends on its

temperature. It is therefore essential to keep humidity

sensors at the same temperature as the air of which the

relative humidity is to be measured.

If the SHTxx shares a PCB with electronic components that

give off heat it should be mounted far away and below the

heat source and the housing must remain well ventilated.

To reduce heat conduction copper layers between the

SHT1x and the rest of the PCB should be minimized and a

slit may be milled in between (see figure 13).

4.5 Membranes

A membrane may be used to prevent dirt from entering the

housing and to protect the sensor. It will also reduce peak

concentrations of chemical vapors. For optimal response

times air volume behind the membrane must be kept to a

minimum. For the SHT1x package Sensirion recommends

the SF1 filter cap for optimal IP67 protection.

4.6 Light

The SHTxx is not light sensitive. Prolonged direct exposure

to sunshine or strong UV radiation may age the housing.

4.7

Materials Used for Sealing / Mounting

Many materials absorb humidity and will act as a buffer,

increasing response times and hysteresis. Materials in the

vicinity of the sensor must therefore be carefully chosen.

Recommended materials are: All Metals, LCP, POM (Delrin),

PTFE (Teflon), PE, PEEK, PP, PB, PPS, PSU, PVDF, PVF

For sealing and gluing (use sparingly): High filled epoxy for

electronic packaging (e.g. glob top, underfill), and Silicone.

Outgassing of these materials may also contaminate the

SHTxx (cf. 4.2). Store well ventilated after manufacturing or

bake at 50°C for 24h to outgas contaminants before

packing.

4.8 Wiring Considerations and Signal Integrity

Carrying the SCK and DATA signal parallel and in close

proximity (e.g. in wires) for more than 10cm may result in

cross talk and loss of communication. This may be resolved

by routing VDD and/or GND between the two data signals.

Please see the application note “ESD, Latchup and EMC” for

more information.

Power supply pins (VDD, GND) should be decoupled with a

100 nF capacitor if wires are used.

4.9 Qualifications

Extensive tests were performed in various environments.

Please contact SENSIRION for detailed information.

Environment

Norm

Temperature

Cycles

JESD22-A104-B

-40 °C / 125 °C, 1000 cy

Within

Specifications

HAST

Pressure Cooker

JESD22-A110-B

2.3 bar 125 °C 85 %RH

Reversible shift

by +2 %RH

High Temperature

and Humidity

JESD22-A101-B

85 °C 85 %RH 1250h

Reversible shift

by +2 %RH

Salt Atmosphere

DIN-50021ss

Within Spec.

Condensing Air

-

Within Spec.

Freezing cycles

fully submerged

-20 / +90 °C, 100 cy

30min dwell time

Reversible shift

by +2 %RH

Various Automotive

Chemicals

DIN 72300-5

Within

Specifications

Table 9

Qualification tests (excerpt)

4.10 ESD (Electrostatic Discharge)

ESD immunity is qualified according to MIL STD 883E,

method 3015 (Human Body Model at

±2 kV)).

Latch-up immunity is provided at a force current of

±100 mA

note “ESD, Latchup and EMC” for more information.

(1)

The temperature sensor passed all tests without any detectable drift. Package and electronics also passed 100%