The other day, Erhard Wielandt stopped by to discuss, scrutinize and eventually approve the latest modifications and improvements to the extension bridge which comes as an optional extra for the CT-EW1 calibration table.

The extension bridge is required for high-sensitivity seismometers and/or high-sensitivity input amplifiers. If you have a standard 1500 V/m/s sensor and a +- 10V or 20V input, the stock CT-EW1 will suit you just fine, and you will gain nothing (pun intended) from using the extension bridge. But if your sensor delivers kilovolts/m/s and/or your input amplifier clips at the millivolt level, even the slow-motion gear of the stock CT-EW1 will be too much, and you will benefit greatly from using the extension bridge.

While the initial design of the extension bridge worked reasonably (as evidenced in the GERESS tests [see here for details] where the "old" extension bridge was part of the test setup), the new one now works flawlessly.

For more (and larger) pictures, take a look at the Image Gallery.

As a follow-up of last year's international workshop jointly hosted by  CTBTO and the German NDC (National Data Center) at the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) and directed by Prof. Erhard Wielandt, an additional field test of the CT-EW1 Calibration Table was performed by BGR in July 2006.

The previous tests had shown that, while the stock CT-EW1 performed remarkably well for "off the shelf" broadband sensors, there are a few configurations that are simply too sensitive for CT-EW1. High-gain seismometers combined with high-sensitivity inputs would get saturated even with CT-EW1 in low-gear mode.

 Consequently, improvements were made both for vertical and horizontal calibration (as detailed in a different news article). BGR now tested these improvements under laboratory and field conditions:

Workshop participants were given the links to the full results. The upshot of the tests (together with a few more pictures) is shown in the Image Gallery here.