REVISED 12-27-2006


© WELLOG 2006



The resolution of an acquisition system must be compatible with the resolution of the printer or plotter that has been chosen for hardcopy.


Can the printer/plotter used for presentation adequately resolve the data captured by the acquisition system?


How much acquisition system resolution is enough?


Hereís an example:




An HP Desk jet 930C inkjet printer or Printrex C930 Color Thermal printer with an x and y (horizontal and vertical) pixel resolution of 300 Dots Per Inch (300 x 300 DPI). Note also, other printers i.e. Printrex 820 DL/G and 840 DL/G have a lower (200 x 200 DPI) resolution.


An acquisition system having a 12 bit resolution (4096 digital representations of a full span analog signal input).


Horizontal pixel plotting considerations:


The largest track combination is track 2 and track 3. According to API standards that equals 4 inches. The number of possible display pixels over the horizontal length of both of the two tracks is 4 inches x 300 pixels per inch = 1200 pixels. The 4096 voltage levels divided over 300 pixels per inch will require a horizontal track of 13.65 inches. It is impossible to display all 4096 voltage representations within the 1200 pixels available.  The analog input signal must be attenuated by a factor of four. Then, four or more voltage levels will be represented by one pixel position over the 1200 horizontal pixels. The resulting resolution is 1024 pixels over a horizontal scale of 3.41 inches. When the presentation is made over a two inch track, it is possible to see that the input signal would have to be divided by a factor of 8. This scale will give a presentation over 1.7 inches and one pixel will represent 8 different input voltage levels.


A possible solution is to wrap the presentation. For the full 4096 bit levels to be presented over 13.65 inches the trace would wrap 3 times and when using a 2 inch track, the trace would wrap six times. Logs having 6 wraps are very difficult to read. It is difficult to keep track of how many wraps have occurred. This problem can lead to errors in reading and interpreting data.


Vertical pixel plotting considerations:


A number of possibilities exist for vertical plotting scales. Logs can be printed in 1 inch per hundred feet, 2 inches per hundred feet, and 5 inches per hundred feet.


With a sample rate of 10 samples per ft. the 1 inch per hundred feet log produces 10 x 100/1 = 1000 samples per inch.


With a sample rate of 10 samples per ft. the 2 inch per hundred feet log produces  = 10 x 100/2 = 500 samples per inch.


With a sample rate of 10 samples per ft. the 5 inch per hundred feet log produces 10 x 100/5 = 200 samples per inch.


*****Note this last scale is the only scale that this plotter is able to define a pixel for every sample taken.


The physical log presentation of a 10,000 ft. well would be 500 inches. That is 500/12 = 41.7 feet long. Looking at the presentation in terms of sheets of printer paper 500/11 = 45.45 standard 11 inch sheets or if using standard API 6.25 inch logging paper thatís 500/6.25 = 80 sheets.


The 10 sample per inch example will require a plotter having a 1000 DPI capability. A pixel having resolution of 1/1000th of an inch is extremely small.

 Horizontal resolution answer:


 A ten bit acquisition system is adequate for all of the above applications. A ten bit system gives 1024 bit positions over 4 inches x 300 DPI is acceptable with no loss of data. When using a 2 inch track, a compression of less than 50 percent is a nominal compromise.



Vertical resolution answer:


Sample rates of five samples per foot is adequate in order to present samples on 1 inch per 100 feet log without compressing much more than 40 percent of the samples.


For answers to questions about printer resolution vs acquisition system resolution contact info@wellog.com .