Humidity design requirements

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I have to design a electronics device that is specified for environmental operating conditions of 0°C to 60°C with 5% to 95% relative humidity (non condensing).

I think the temperature part should be covered with commercial component selection (0°-70° operating temp.), but what about the humidity requirement?

• Is this humidity specification hard to achieve?
• Do I need to protect the PCBA with conformal coating?
• What are the general recommendations for different humidity specifications?

Of course I will need to perform some tests in the climate chamber. But I think there should exist some general guidelines for the design regarding humidity?specificationshumidityconformal-coatingShareEditFollowFlagasked 5 hours agoStefan Wyss5,25911 gold badge66 silver badges1818 bronze badges

• 1What do you mean by non condensing? I don’t think conformal coating would be adequate. – K H 5 hours ago
• 2I have often seen this “non condensing” addition to relative humidity specifications. I think it means that when you perform tests in the climate chamber, you need to carefully control the climate in order not to reach the dew point. – Stefan Wyss 5 hours ago 
• Well, you can easily find a cheapy commercial humidity sensor chip, and copycat its spec. Eg, (1) HDS1080 [0% to 100% relative humidity (Fig 2, 14 bit, 2~4% accuracy )] from TI:ti.com/lit/ds/symlink/… – tlfong01 5 hours ago    
• 1If you have high impedance analogue and sensitive circuits, at around 0 degC, water will collect on PCB surfaces if there’s humidity. So, I’d be tempted to ensure it works down to -10 degC and see what happens when you gradually warm it up through 0 degC. – Andy aka 4 hours ago
• 1@Andyaka Thanks for your comment. I have no high impedance analogue and sensitive circuits. It is mainly a digital device. Why do you think that 0°C will be special in term of humidity? When I look at a psychrometric chart, I see no differences to other other temp. ranges. – Stefan Wyss 4 hours ago 
• I don’t understand the difference between condensing and non condensing, but condensing modules are dirt cheap. (1) HR202 Sensor HDS10 Condensation Sensor Humidity Sensitive Module High Humidity Sensitive US$0.30 nl.aliexpress.com/item/… / ton continue, … – tlfong01 4 hours ago    
• / continue, … (2) Humidity Sensor Module HR202 Humidity Module Humidity Detection – US$0.5 nl.aliexpress.com/item/… – tlfong01 4 hours ago   
• Actually I even forgot the difference between H and RH. Of course Google is my friend: (3) Choosing a Humidity Sensor: A Review of Three Technologies – Denes K. Roveti 2001jul01 fierceelectronics.com/components/…. Now I understand everything, including that the US$0.5 toy understands the First and Second Law of Thermodynamics and has a built in EEPROM with equations to do the RH calculations. – tlfong01 3 hours ago    
• 1@StefanWyss – ice that forms on PCB surfaces at below 0 degC starts to melt and becomes more conductive as temperature passes positively through 0 degC and I’ve had problems with that before that have been cured by varnish/lacquer. – Andy aka 3 hours ago
• @tlfong01 I do not understand why you are proposing a humidity sensor when I‘m asking for advice on humidity design requirements? – Stefan Wyss 1 hour ago
• @Stefan Wyss, Ah, there is some misunderstanding. I know you are asking (1) If the 5% ~ 95% relative humidity specification is hard to achieve, and (2) If there are general recommendations for different humiudity specifications. My first thought is that your specification is too linent. So I am recommending two example cheap humidity sensors for you to compare their much more strict user requirements. / to continue, … – tlfong01 1 min ago   Edit   
• / cont’d … These two example, commercially available cheap sensors should also meet the general user requirements and can be practically implemented using 16 bit ADC, and EEPROM with humidity calculations etc. My apologies for misleading you that I am recommending sensors for you to purchase. Have a great project. Cheers. – tlfong01 just now   Edit   

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