“Which hygrometers are the most precise, the ones with real or synthetic hair?“ Mr. Wolfgang Pech asked us.
The measurement accuracy of a hygrometer is not just influenced by the kind of hair which is used. It is much more important how good the humidity addicted length variation of the hair is transmitted to the needle. So you can’t say that real hair is always more or less precise than synthetic hair.
The decision which kind of hair will be used is depending of the operating site of the hygrometer:
Real hair hygrometers react really fast at humidity changes and are also good to use at low temperatures (operating area: -35 … +65 °C). They are the only mechanical hycrometers to be used senceful below 0 °C. Everything else would react way to sluggish. Indeed the indicator stability of a real hair hygrometer is just given if the hair regenerates regularly. For that it needs to be in high humidity. This is no problem with outside used hygrometers as the humidity during the night is naturarely high. In this case no maintenance is needed. At inhouse use that is not given why it is necessary to put the hygrometer into high humidity minimum once in three weeks. One method is the so called “humidity package”: Put the hygrometer in a warm and humid towel for at least 30 minutes. You could take it to the bathroom with you while taking a shower. Or leave it outside during night.
As the maintenance effort is relatively high, we suggest the use of an hygrometer with synthetic hair for indoor climate measurement. It also can be used at higher temperatures (normal 0 … 70 °C, but also up to 120 °C with special pretreatment, for example in saunas). The synthetic hair is free of maintenance effort, you don’t need to get it humid regularly. But we still recommend to do it ones or twice a year.