Cumulus Support

Hi

I have decided to run a little test of the accuracy of the temperature sensor/hygrometer. I currently have a WMR88 temperature sensor (Sensor 1) housed in a small wooden radiation screen and I have now added to the radiation screen a small cheap LCD temperature sensor/hygrometer from eBay which also has a Max/Min function and I shall now refer to as Sensor 2.

Observations so far:

1. Sensor 2 seems to respond more rapidly to temperature changes than Sensor 1 (i.e. when being handled)

• Sensor 2 consistently reads temperatures 0.6 °C to 1.1 °C lower than Sensor 1 and humidity the same or slightly higher.

• Sensor 2 temperatures are closer to readings from the local official Met Office site

09/04/14 1200L: Sensor 1 = 14.6 °C Sensor 2 = 13.8 °C
09/04/14 2000L: Sensor 1 = 13.7 °C Sensor 2 = 12.7 °C
10/04/14 0800L: Sensor 1 = 5.6 °C Sensor 2 = 4.7 °C
10/04/14 2100L: Sensor 1 = 11.9 °C Sensor 2 = 11.0 °C
11/04/14 0700L: Sensor 1 = 9.5 °C Sensor 2 = 8.4 °C
11/04/14 1700L: Sensor 1 = 14.9 °C Sensor 2 = 14.1 °C

I know it's only a relatively small difference but it seems strange considering both sensors are in the same screen and about 1 inch apart. Could it be that the cheaper LCD sensor is more accurate?

The only way to find out would be a third sensor and see if it agrees with one of the other two.
As for agreeing with met office, there are so many factors that affect temperatures that you probably would get different readings from one side of your house to the other other, never mind a few miles away.

Martin

Yes I was thinking the same thing. I need a 3rd sensor of a different kind (maybe a mercury thermometer) or a sensor produced by a different manufacturer.

Thanks,

Callum

There are types of sensors that work differently. It's possible your LCD sensor uses the same kind of sensor that is used in vehicles and things like industrial fridges, that need rapid response, and aren't really made to be used in a meteorological environment. It could explain the differences, especially the differences in response.
I'd say that the Oregon sensor is more accurate, also because of the "slowness" it responds with, as to probably measure a more accurate figure, and not a snapshot like the LCD sensor probably does.

For what it is worth I have compared my WMR88's wireless thermometer to a calibrated digital thermometer I own and the results were almost identical. Pretty good for a station that only cost £59.99 in my opinion. It was also very close to my old 1-wire system which I have kept running.

The only thing I did notice is it doesn't pick up small quick spikes, which I pesume is because the sensor is inside the pastic case where as my calibrated one has a probe and my 1-wire was simply at the end of the wire with no case. I know some people do mod their sensors to expose the actual sensor more which would probably help.

I have no way to test the humidity sensor though.

I've always said good sensor location and shielding is more important than a sensor being +-0.1 degrees correct for an ammeter observer anyway.