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4. If the update time is unacceptable, adjust the resolution and circulations to lower the update time.
You can make a note of the parameters as you go along:
Number of bits required:
Resolution (R):
Circulations (N):
Update Time: less than ms.
Table 1A Calculations for Required Binary Bits
Binary Bits Maximum Count Maximum Stroke (in.), Maximum Stroke (in.),
w/0.001 in. Resolution w/0.0005 in. Resolution
14 16,383 16 8
15 32,767 32 16
16 65,535 65 32
17 131,071 131 65
18 262,143 262 131
19 524,287 524 262
20 1,048,575 - -
Table 2A Circulations vs. Resolutions
Resolution Circulations (N)
0.004 1
0.002 2
0.001 4
0.0005 8
0.00025 16
0.000125 32
NOTE:
Values in Table 2A are based on 27-28 MHz clock.
Example 1
Given:
• Stroke: 48 in.
• Resolution: 0.001 in.
• Maximum Update Time: 3 milliseconds
1. 48 ÷ 0.001 = 48000 counts. From Table 1A, this requires 16 bits.
2. From Table A-2, N = 4.
3. The graph (Figure A-1) indicates an update time of approxi-
mately 2.3 milliseconds (which is acceptable).
4. Repeat Steps 1 to 3 for half the resolution (0.0005 in.), to pro-
vide increased stability for the 0.001 in. least significant bit.
Notice that for 0.0005 in. resolution, N = 8 and the update time
exceeds the specified maximum of 3 ms. Therefore, specify
N=4 and 0.001 inch resolution.
Specify:
Number of bits required: 16
Resolution: 0.001 in.
(Re)circulations: 4
Update Time: less than 3 ms
Figure A-1
Update Times (external interrogation)
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