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A few thoughts and recommendations on setup. The photo above shows the solar image properly "split" by the analemma, for scale, the analemma is .05" (1.3mm) wide and the solar image is .1" (2.5mm) in diameter. * Note the penumbra effects of the sight shadow vs. the image! Our heliochronometers are very precise instruments, the accuracy that you achieve depends directly on the stability of the plinth (base) provided, and the amount of time that you are willing to devote to the setup of the instrument. To make this process as easy and rewarding as possible we would like to share some tips we have found useful. Above all, the plinth should be stable. Orientation and level are secondary to the stability of the plinth. Level and directionality are more easily achieved by an intermediate plate, using a 3 point system with a fine adjustment for the North / South orientation. If you have purchased one of our sub-plates please refer to the documentation provided with that product. If you are providing the intermediate plate, we would suggest that they be made from material that is corrosion resistant, and be at least twice the thickness of the screws that will secure them (a plate using 6mm screws should be at least 12mm thick, if using ¼" screws then at least 1/2" plate should be used). After transferring the bolt pattern to secure the heliochronometer to the plate, 6 additional holes are needed in the sub-plate, 3 should be threaded (fine threads provide easier and more precise adjustment) and 3 of these should be for clearance only. The pattern should be in the form of a triangle with the "base" of the triangle facing the south (north in the Southern Hemisphere) and the apex facing north. The threaded holes should be outboard of the clearance, or clamping holes, but in line with, and as close to, the threaded holes as practical in order to minimize distortion when tightened.
Here is a drawing: Stage I setup: Using the markings on the Heliochronometer, set the latitude and longitude with the scales provided on the instrument. Next, level the base plate with a bubble or spirit level (this should be as close as possible at this stage)and mount the instrument on the sub plate. At this point you must find the true North South line. This can be accomplished in several ways: a precision compass, GPS, or with the heliochronometer. If you wish to use the instrument, then you must obtain the time of solar noon at your location for the specific date that you will be setting up. Solar noon for your particular location can be found in almanacs, on the Internet, or through your local airport or university. Once you know the time of solar noon for your locality, align the shadow cast by the latitude ring on the body of the ring clamp so that the shadow is bisected by the two halves of the clamp. Stage II setup: At this stage of the setup you should watch the "standard time" reported by the instrument for 2 or 3 days. The times reported vs. clock times are not as important as a deviation between morning vs. evening time discrepancies. Equal discrepancies in morning/ noon/ evening times indicate a problem with the latitude adjustment. Discrepancies that accumulate during the day indicate a problem with the East / West Level or the North / South orientation of the instrument. First check the North / South orientation by the "solar noon" method. If you are convinced that this is correct after a few observations, then begin "splitting the difference" through progressively re-leveling the sub plate in the East / West orientation. Be sure not to disturb the North / South level during this process, keep adjustments of the screws at the base of the "pyramid" equal and check with a level in that plane after adjustments. Once you have "tuned out" the variations during the day, set the vernier to the correct standard or daylight savings time. Here in Arizona there is no daylight savings time adjustment, so it is a non-issue here, but in order to be in step with the rest of the world, daylight savings adjustment is available on all instruments. On Aten and Aten I models this is accomplished by an additional set of threaded holes on the bottom of the hour ring, offset by 15 degrees. On Aten II and Classic models the same function is accomplished by the plate that the scale is attached to. Users in the higher latitudes may want to consider setting the instrument to daylight savings at setup and leaving it there, or just adding 1 hour mentally during the suitable times. It is, of course, up to the discretion and preferences of the user. Stage I setup should be within +- 1.5 min. during a day. Stage II setup should be within +- 30 sec. during a day Stage III setup: optional For the truly obsessive among us (we know who we are) there is a further refinement to this process, and it will result in even greater accuracy. If you happen to be setting up between 30 and 50 degrees of latitude (the closer to 40 the better), our heliochronometers can be tweaked into the realm of +- 5 - 15 sec. accuracy. This is easiest to accomplish with the Aten II due to the larger scale and greater length of the focal plane, but is possible with all models under the right circumstances. 5 seconds is a very small fraction of a degree (about .021 ), so this requires a crystal clear day and works between the hours of 8/9am to 3/4pm, depending on latitude. To do this you will need a few things: a CAD package that will read DXF files is very helpful, a precision level (.0005" per Ft.), a precision spirit compass (.01 deg.) and a dial, vernier, or digital caliper. You have a small flat area on the top of your analemma, this is a "reference plane". Using this, it is possible to measure the distance from the plane to the center of the solar image. This distance is a known quantity for every date. We will be happy to supply it as a CAD file (dxf or iges) or as a simple text file consisting of the X and Y coordinates for each day of the year and the distance of the reference plane to X0,Y0 - this is marked on the analemma engraving by the small point between the E and Q denoting the equinox lines. To obtain these files for your heliochronmeter send us an e-mail and be sure to include your serial number so the information provided will be correct. Using this distance as an optimum, the dial can be "tweaked" by using orientation and level to produce a condition where the solar image measures consistently on the mean distance at sunrise, noon, and sunset thus "tuning out" or Canceling any anomalies. With this accomplished, "set" the instrument to a time slightly in advance of the current time and watch the solar image as it advances across the analemma until it is bisected by the line. This technique eliminates the need to "read between the lines" in order to determine time periods smaller than 20 seconds. |