FRINGE SAMPLING

Last update: August 1997

A different program controls the camera for sampling the fringes. It is also in the "c:\nic_code directory" and it is presently called "fringes5".
The pixels to be sampled are specified in the frnges5.cfg file; and they are the only parameters you need to change there.
As before, you get out of fringes5 by typing "Shift-S", and then choosing to continue with different parameters or quitting.
This program reads the two selected pixels and sends the data to the data acquisition Quadra, which displays it and saves it to disk if so desired.
You must first start the fringes5 program and THEN start the Quadra program (MacInscope1.1.0); the actual sampling of the nicmos and sending of the data starts when you turn on the piezo scanner electronics (each scan is triggered by the piezo sending a TTL signal to the Quadra when it stars on its 60 micron trip). The display on the Quadra shows the two raw data outputs (complementary fringes), on a scale 1-65535, when the gain is set to 1; and the difference between the two fringes normalized by a dc average, and filtered if you so choose. The sky background is not subtracted. If the background were a small contribution, a 100% fringe would be full scale on the plot showing the difference fringe.
For historical reasons (the program running in the Quadra was inherited from the visible experiment) the nicmos sampling must send exactly 256 data points to the Quadra; which imposes some limitations on the fringe sampling modes. Most notably, it implies that :

The readout mode is specified by selecting a number of reads per sample and a number of samples per frame; I call a frame the final average of (reads per sample x samples per frame) for both pixels.
While the Pentium samples the two pixels in the selected mode, the short delay line line is following the sidereal fringe position, and the piezo mirror is passively scanning its 60 microns of max. range at a frequency that must be selected, and which determines the fringe frequency together with the wavelength and sampling time.
These are some calibrated modes :

Samples/Frames	Reads/Sample	Set Scanning Freq. to	Sampling Time
4	4	1.9 Hz	1.03 ms
3	4	2.6	0.75
2	4	3.7	0.52
1	4	7.6	0.25
1	1	10.6	0.18

For a given choice, you must actually go and set the piezo scanning freq. to the appropriate value on the piezo electronics box. You can monitor its value by looking at the driving waveform on the cope.
The fringe frequency can be determined in each case from the above sample rates (in samples/fringe) for each spectral band and the above sampling times as :

Fringe Freq. = 1/(Samp. Rate x Samp. Time)

You must establish communication between the Short Delay Control Quadra and the Data Acqusition Quadra so that you get the correct header information in your files.
To quit the program, the less violent way is to stop the piezo scanner electronics (stop the TTL signal), then quit the fringes5 program on the Pentium and then quit the MacInscope program on the Quadra. Then turn off the camera power supply.

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