Hi to all users!
I was taking a look to geophone parameters (natural frequency, damping, coil resistance, sensitivity) on datasheets.
All these parameters are reported at specific temperature (usually 20 °C) but geophone can be installed in different free field conditions (up to 60 °C on summer, up to -20 °C on winter, even if I try to place thermal insulation, my Shake died last summer in a metallic box placed on direct sunlight, peak temp was over 50 °C!!!).
How does this parameters change with temperature?
Are there studies about this?
Is coil resistor linear with themperature?
And what about damping?
Thanks.
Hello 3lB3rt0, welcomet to the community!
Yes, all the values of geophones are indicated, as you said, with a temperature of usually 20 °C, and your following observations are correct.
We use a RGI-20DX 4.5 Hz, 395 Ohm, Vertical Racotech Geophysical Instruments geophone, https://raspberryshake.org/learn-support/diy-tutorials/ and here you can find its technical sheet: https://raspberryshake.org/wp-content/uploads/2020/05/racotech-geophone-datasheet.pdf
The company that supplies these to us guarantee their nominal performance in a temperature range of -40℃ to +80℃ but there are studies on the fact that the change in temperature can affect the sensitivity of the geophone itself, like it can be read here: https://www.ndt.net/article/jae/papers/23-081.pdf
There are also geophones that are guaranteed to work at very high temperatures, like 200°C: https://www.iongeo.com/virtuals/ResourceArchives/content/documents/Resource%20Center/Brochures%20and%20Data%20Sheets/Data%20Sheets/Sensor%20Geophones/DS_SEN_121023HITEMP.pdf
From what I can see, the coil resistance is usually linear with temperature, while the damping can be assumed as linear, even if it is not properly so.
If you want to expand more on these specifications, as they are outside our control (since we acquire the geophones from that company) I encourage you to contact them and aks for more details.
Thanks for answer.
At first link we are talking about a 10Hz geophone with 1200 Ohm coil resistance (and no data, just simple graphs).
As I can see, from 20°C to 60°C (let’s say maximum temperature), Rcoil (from 900 to 1100) is about +20% from nominal value… I think it’s a lot.
On second link there is no 4.5Hz geophone.
I understand I try to build thermal-insulated location for geophone but I’m surprised there are no studies about this…