User guide

Appendix D
Estimating Scan Time
D–5
Worksheet C — Estimating the Scan Time of Your 1747–L524 Processor
Procedure Min Scan Time Max ScanTime
1. Estimate your input scan time (µs).
A. Calculate the processor input scan of your discrete input modules.
Number of 8 point modules ________ x 126 = a.)________
Number of 16 point modules ________ x 195 = b.)________
Number of 32 point modules ________ x 335 = c.)________
B. Calculate the processor input scan of your specialty I/O modules.
Number of 1/4 DCM or analog combo ________ x 375 = d.)________
Number of 1/2 DCM, analog input, 1746–HS ________ x 659 = e.)________
Number of 3/4 DCM ________ x 944 = f.)________
No. of full DCM, BASIC small config., or 7–block DSN ________ x 1228 = g.)________
Number of 1747–KE ________ x 250 = h.)________
C. Calculate the processor input scan of your specialty I/O modules.
Number of BASIC Lg. config., 1746–HSCE ________ x 1557 = i.)________
Number of RI/O Scanner or 30–block DSN ________ x 4970 = j.)________
D. Add lines a through j. Place this value on line (k).
Add 121 to the value on line (k). This sum is your minimum input scan time. k.)________ + 121 =
E. Calculate the maximum input scan time:
Minimum scan time + (Number of specialty I/O modules in part B x 30) + (Number of specialty I/O modules in part C x 120)
F. Calculate Forced Input Overhead = (No. of input modules x 108) + 140 per additional word for multi–word modules
_________
_________
_________
2. Estimate your output scan time (µs).
A. Calculate the processor output scan of your discrete output modules.
Number of 8 point modules ________ x 104 = a.)________
Number of 16 point modules ________ x 164 = b.)________
Number of 32 point modules ________ x 282 = c.)________
B. Calculate the processor output scan of your specialty I/O modules.
Number of 1/4 DCM or analog combo ________ x 372 = d.)________
Number of 1/2 DCM, analog output, 1746–HS ________ x 617 = e.) ________
Number of 3/4 DCM ________ x 862 = f.)________
No. of full DCM, BASIC small config., or 7–block DSN ________ x 1047 = g.)________
C. Calculate the processor output scan of your specialty I/O modules.
Number of BASIC Lg. config., 1746–HSCE ________ x 1399 = h.)________
Number of RI/O Scanner or 30–block DSN ________ x 4367 = i.)________
D. Add lines a through i. Place this value on line (j).
Add 138 to the value on line (j). This sum is your minimum output scan time. j.)________ + 138 =
E. Calculate your maximum output scan time =
Minimum scan time + (Number of specialty I/O modules in part B x 30) + (Number of specialty I/O modules in part C x 120)
F. Calculate the Forced Output Overhead = (No. of output modules x 104) + 140 per additional word for multi–word modules
_________
_________
_________
3. Estimate your program scan time. This estimate assumes operation of all instructions once per operating scan.
A. Count the number of rungs in your APS program. Place value on line (a).
B. Multiply value on line (a) by 6. (If you saved your program with Single–Step Enabled, then multiply the value on line (a)
by 66.) a.)________ x 6 =
C. Calculate your program execution time when all instructions are true. (See appendix A to do this.)
4. Add the values in the minimum and maximum scan time columns.
__________
__________
________
__ subtotal
_________
_________
_________ subtotal
5. Add processor overhead time (180 for min. scan time; 280 for max. scan time) to the subtotals estimated in step 4.
Use these new subtotals to calculate communication overhead in step 6.
+ 180
________subtotal
+ 280
_________ subtotal
6. Estimate your communication overhead:
A. Calculate the background communication overhead: multiply the subtotal for minimum scan time (estimated in
step 5) by 1.040; multiply the subtotal for maximum scan time by 1.140 (max. value accounts for active DH–485 link).
B. Calculate the foreground communications overhead: for minimum scan time add 0; for maximum scan time
add 2286. (Maximum scan time accounts for programmer being attached to processor.)
C. Convert
µsecs. to msecs., divide by 1000.
x 1.040
_________ µsecs.
+ 0
__________ µsecs.
/ 1000
x 1.140
_________ µsecs.
+ 2286
_________ µsecs.
/ 1000
Estimated minimum and maximum scan times for your 1747–L524 series C application:
msecs. msecs.
7. Estimate the scan time for your 1747–L524 series B application; multiply the values for series C application by 0.60.
Estimated minimum and maximum scan times for your 1747–L524 series B application:
x 0.60
msecs.
x 0.60
msecs.