S 1
S 2
S 3
R
T S
D E L AY
(5 8 )
N
The time delay function code provides a pure delay on an analog signal. It can be used to create fixed or variable time delays, or model systems that represent dynamic time delays.
Outputs
Blk
N
Type
R
Description
Time delayed function of input
Specifications
Range Description
Note 1 Block address of input (X)
Spec Tune Default Type
S1 N 5 I
S2
S3
N
N
6
1
I
I
Note 1 Block address of rate input (R, in units/sec)
Full
Note 1 Block address of track switch signal:
0 = track
1 = release
Length of queue (L, in units)
0 - 255 Number of intervals (N)
S4
S5
N
N
NOTES :
1. Maximum values are:
0.000
1
R
I
9,998 for the BRC-100, IMMFP11/12
31,998 for the HAC
S1 – <X> Block address of the input.
S2 – <R> Block address of rate input in units per second.
S3 – <T> Block address of track switch signal.
0 = track input
1 = release
When <S3> = 0, it initializes all n elements of the memory to the input value:
Then M
1
= M
2
= ...M
n
= <S1>, and elapsed time since the last sample = 0.
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58 - 2
There is no time delay.
If <S3> = 1, then:
Time Delay =
á
S
S
4
2 ñ
Time Interval (TI) =
S 5
Elapsed Time = ET + t where: t
ET
TI
Mi
Time since last sample in seconds
Time since last algorithm execution in seconds
Internal input sample time in seconds
Memory locations where input values are stored during the time delay
If ET ³ TI:
M i
= M i
M n
+ 1, for i = 0 to n
= output value, and M
1
= <S1>
Elapsed time = ET – TI
S4 – L (Length of queue) Length of the queue in units. The queue is the number of units over which the time delay is effective.
S5 – N (Number of intervals) Number of times, from one to 190, that the input is to be sampled. Determine N by dividing the time delay (TD) by the desired sampling frequency.
For a fixed time delay, the rate input, <S2>, is constant. The time delay between output and input varies only with S4. It is directly proportional to S4. For example, simulate the time delay for flow through a pipe. Assume a required time delay of two minutes with input sampling desired every five seconds.
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IN P U T
Select the default value of 1.0 (found in fixed block six) for
<S2> since rate is constant for fixed delays.
<S2>
S4
S5
Time Delay
TD
TD
120
S4
= Rate in units per second = 1.0
= Length of the queue in units
= Number of intervals
= 2 minutes = 120 seconds
= 120 seconds
=
-------------
S 2 ñ
= S 4
---------
1.0
= 120 units = Length of queue
For input sampling every five seconds:
N =
TD
---------------
5 sec
120 sec
----------------------
5 sec
=
= 24 intervals
Figure 58-1 is an illustration of this example.
T /N
O U T P U T
0 1 2 3 N
L
T 01 65 1 A
Figure 58-1. Fixed Time Delay Example
Variable time delays may be dynamically adjusted by changing the value of <S2>. Using a function code 9 block, as illustrated in Figure
58-2
, the two fixed input rates can be switched. In the fixed time delay example, when <S2> equals 1.0, the time delay, S4/<S2> equals 120 seconds. By changing <S2> to 2.0, the time delay becomes 60 seconds, and the timing interval,
TD/N equals 2.5 seconds. Changing the rate input <S2> while holding all other parameters constant changes the timing
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58 - 4 interval. Faster rates produce more frequent input sampling, and slower rates produce less frequent input sampling for the same number of intervals.
A
A
(2 )
15 0
S 1
S 2
S 3
(2 )
15 5
LO G IC S IG N A L
C ON T R O LL IN G
TR A C K S W ITC H
T-IN T
(13 )
16 0
S 1
S 2
S 3
R
T S
D E L AY
(58 )
1 6 5
T 01 65 2 A
Figure 58-2. Variable Time Delay
The analog time delay block may be used to model a physical system that represents a dynamic time delay. For example, an oil pipeline may have a measurement device at a different location than the indicator/controller. With this function code, a measurement can be taken. This function code delays sending the value to the controller until the element of oil reaches the controller. Specification 4 may be specified in feet, <S2> in feet per second, and N to establish the needed resolution.
If S4 = 100 feet and <S2> varies from ten feet per second to 20 feet per second, then TD will vary between ten seconds and five seconds.
If sampling is required every 0.5 seconds to achieve the needed resolution, then:
N =
=
= longest time delay
------------------------------------------------
0.5
sec
10 sec
0.5
sec
20
intervals
The longest time delay can present a worst case scenario. No matter what the time delay, the input will be sampled 20 times over that period to insure adequate resolution.
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For the shortest time delay, the sampling intervals will be:
5 sec
------------------------------
0.25 second
20 intervals
=
In most cases, the delay in a process consists of more than a pure time delay (deadtime). There is usually an additional time lag that may be a first, second, or higher order lag. In general, the process responds to a second order lag response. This can be simulated accurately by using a time delay and a first order lag. If necessary, another first order lag function block can be added. Figure
58-3 shows a graphic representation of a func-
tion and a simulated response. Figure
58-4 illustrates the con-
figuration required to simulate the response shown in
Figure
58-3 .
IN P U T
O U T P U T
T Y P IC A L
R E S P O N S E
F IR S T O R D E R
S IM U LAT E D R E S P O N S E
T IM E
Figure 58-3. First Order Simulated Response to Typical Time Delay
T 01 65 4 A
S 1
S 2
S 3
R
T S
D E L AY
(5 8 )
1 5 0
S 1
S 2
F (t)
(3 )
1 5 5
S 1
S 2
F (t)
(3 )
1 6 0
T 0165 3 A
Figure 58-4. Response Simulation Configuration
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