Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 70)

Programming
Chapter 3
3Ć27
an implied decimal point. the x10 multiplier bit is B12 in word
W19(W39). Range is 00.10 to 999.9. a value of zero implies no filter.
W21 (W41) Maximum Negative Error, EMN. This word contains the
maximum negative error for the loop. This value can be used for alarm
purposes and/or limiting. The alarm condition is indicated by
W61(W68)B15. error limiting is selected by B12 = 1 in word
W18(W38). Data format is 4-digit BCD with a range from 0000 to 4095.
a negative value is implied.
W22(W42) Maximum Positive Error, EMP. This word contains the
value used as the maximum positive error for the loop. This value can be
used for alarm purposes and/or limiting. The alarm condition is indicated
by W61(W68)B14. Error limiting is selected by B12 = 1 in word
W18(W38). Data format is 4-digit BCD with a range from 0000 to 4095.
a positive value is implied.
W23(W43) Dead Band, DB. This word contains the error dead band
value. This value can be used for alarm purposes and/or setting the dead
band range. The error dead band extends above and below zero error so
that the dead band range is twice the dead band value. Dead band is
selected by B11 = 1 in word W18(W38). The alarm condition is indicated
by W61(W68)B11. Data format is 4-digit BCD with a range from 0000 to
4095 above and below zero error.
Any time the error value is outside the dead band, the actual error value
will be used for computational purposes. As it crosses into the dead band,
the error value continues to be used for computational purposes until it
crosses zero. Once it crosses zero and as long as it remains in the dead
band, the error value will be set to zero for computational purposes.
W24(W44) Integral Gain, K I (Reset Term 1/T I). If W02B00 is reset,
the module uses the A-B value K I and this word contains the integral
gain constant for the loop. If W02 B00 is set, the module uses the ISA
value I/T I and the word contains the reset term for the loop. Data format
is 4-digit BCD, 9.999 in units of inverse seconds (A-B) or inverse minutes
(ISA), with implied decimal point. Multiplier bits W19(W39)B03, B02
can be selected for x1, divided by 10, x10, x100 (Table 3.F). By using
multipliers, the range can be extended from .0000 to 999.9.
The integral term K I or reset term 1/T I must be greater than zero for the
module to perform bumpless transfer. Reset or hold the integral term V I
to zero by setting K I or 1/T I = 0.