Temperature Measurements using Gemini Miniature Data Loggers

Ole Humlum, The University Courses on Svalbard (UNIS), Norway.

General

Gemini data loggers comes in several varieties, precipitation, humidity, movement, shock and temperature. Only temperature data loggers with external sensor will be discussed at this place.

The logger unit

Presently, the 12-bit Gemini temperature data loggers (Tiny Tag Plus High Resolution) with external sensor probe measures over the range –40^oC to +125^oC. The logger itself may not work properly if operated outside a temperature range from –40^oC to +85^oC. They are waterproof to 15 m (50 ft), measures 34 x 59 x 80 mm and weights 110 g.

The resolution on the individual readings is 12 bit. The logging interval is user-controlled and may be set from 1 sec to 10 days. There are several start options: now, delayed (up to 45 days), event, magnetic impulse. Stop options: when full, after N readings, never (wrap around). Reading type: actual, min or max. The logger may be offloaded while running when logging in minute multiples.

All programming and offloading of the logger is done by means of easy-to-use Windows-based software.

Memory

The logger has an internal memory of 32k (EPROM; non-volatile), storing about 16,000 readings. If the logger is programmed to take hourly readings this corresponds to almost two years of service, or you may obtain 5 month data at 15 minute intervals. 

Battery

The logger uses Saft 3.7V 1/2AA Lithium cells, having a battery life up to 5 years. However, battery replacement is recommended every 2 years. The logger should be stopped before replacement. A complete Tinytag Plus Service Kit including battery, seal and silica gel pack may be obtained from the firm.

External sensor probe

The external sensor probe (type: 10k NTC thermistor) is connected to the logger by a 3 m cable and measures 5 x 150 mm. The measuring range is –40^oC to +125^oC. The response time is 45 sec in air and 20 sec in water. The accuracy is about ±0.2^oC.

Price

The current price (December 2000) is about US $ 200 for the logger unit and about US $ 22 for the probe. The Gemini Group are based in UK, but you may obtain the logger and probe from local distributors in several countries. Please check the Gemini homepage for further details.

Special notes

When using the logger at low temperatures, condensation may form inside the chase. Therefore, before opening the chase for any reason (e.g., battery replacement), allow the unit to reach the room temperature if the operation is carried out indoor. You need no open the chase for offloading of data.

When using the logger and sensor probe in a wet or humid environment (water or melting snow pack) you should take care to ensure that the connector cap (for offloading) and sensor probe are securely fitted. Silicone may with considerable success be applied at these points.

This type of data logger have been used with satisfactorily results for several years in Greenland, the Faroe Islands, Scotland, Denmark and on Svalbard. The EPROM memory ensures that you often will be able to recover data from a logger which accidentally has been water filled. After proper drying and battery replacement you may even succeed in reviving the logger after such an event! 

Latest update: 3. July 2001.