IDEC FC4A-C10R2 User Manual page 193

Timer Accuracy, continued
Timer Counting Error
Every timer instruction operation is individually based on asynchronous 16-bit reference timers. Therefore, an error occurs
depending on the status of the asynchronous 16-bit timer when the timer instruction is executed.
Error
Advance error
Maximum
Behind error
Timeout Output Error
The output RAM status is set to the actual output when the END instruction is processed. So, an error occurs depending on
the timing when the timeout output turns on in a scan cycle. The timeout output error shown below does not include output
delay caused by the hardware.
Program Processing
Timeout Output RAM
Actual Output
Maximum and Minimum of Errors
Error
Advance error
Minimum
Behind error
Advance error
Maximum
Behind error
Notes: Advance error does not occur at the timer input and timeout output.
Tet + Tte = 1 scan time
Increment is 1 sec (TML), 100 ms (TIM), 10 ms (TMH), or 1 ms (TMS).
The maximum advance error is: Increment – 1 scan time
The maximum behind error is: 3 scan times
The timer input error and timeout output error shown above do not include the input response time (behind error)
and output response time (behind error) caused by hardware.
Power Failure Memory Protection
Timers TML, TIM, TMH, and TMS do not have power failure protection. A timer with this protection can be devised using
a counter instruction and special internal relay M8121 (1-sec clock), M8122 (100-ms clock), or M8123 (10-ms clock).
Ladder Diagram
(10-sec Timer)
Reset
CNT C2
1000
I1
Pulse
M8123
TML
(1-sec timer)
1000 ms
1 scan time
END TIM
ON
OFF
ON
OFF
Tte
1 scan time
Timer Input Error
0 (Note)
Tet
0 (Note)
1 scan time + Tet
Program List
Instruction
LODN
LOD
CNT
Note: Designate counter C2 used in this program as a keep type counter. See page 5-4.
« FC4A M
TIM
(100-ms timer)
100 ms
1 scan time
END
Timeout output error is equal to Tte (behind error) and can
be between 0 and one scan time.
0 < Tte < 1 scan time
Tte: Time from the timer instruction execution to the END
processing
Timer Counting Timeout Output
Error
0
0
Increment
1 scan time
Data
I1
M8123
C2
1000
S U ' M
ICRO MART SER S ANUAL
7: B
ASIC
TMH
(10-ms timer)
10 ms
1 scan time
Error
0 (Note)
Tte
0 (Note) Increment – (Tet + Tte)
Tte 2 scan times + (Tet + Tte)
Timing Chart
ON
I1
OFF
10 sec
ON
C2
OFF
»
I
NSTRUCTIONS
TMS
(1-ms timer)
1 ms
1 scan time
Total Error
0
0
7-9