The Analog Property component in the DCS library holds a value from an upstream component. The Analog Property works with double value types. The Analog Property has no execution number thus it can not read or write a value. It relies on the upstream component to write to it and the downstream component to read from it. Two Analog Properties can not be linked together.

The Digital Property component in the DCS library holds a value from an upstream component. The Digital Property works with digital values (0 and 1). The Digital Property has no execution number thus it can not read or write a value. It relies on the upstream component to write to it and the downstream component to read from it. Two Digital Properties can not be linked together.

The HMI Integer Property component in the DCS library holds a value from an upstream component. The HMI Integer Property works with integer value types. The HMI Integer Property has no execution number thus it can not read or write a value. It relies on the upstream component to write to it and the downstream component to read from it. Two HMI Integer Properties can not be linked together.

Type Conversions

The Analog to Digital component of the DCS library converts an analog value at the input port to a 16 bit digital value. There are 16 output ports (for bit 0 to bit 15).

The Digital to Analog component of the DCS library converts a 16 bit digital value at the 16 input ports (for bit 0 to bit 15) to a 16 bit digital value. There are 16 output ports.

The Double to Integer component of the DCS library returns a 1 when the input value is equal or more than to 0.5 and returns a 0 when the input value is less than 0.5. This is used where a double to integer link (Section 1.5) is used and the correct rounding is to be done. The double to integer link throws away all decimal values. This decimal value can be used as the input to the Double to Integer component and the rounding will be done according to the criteria explained above. The output value must then be added to the integer value. This can also be required where analog to digital conversions is done to carry the correct rounding value across.

The Integer to Double component of the DCS library returns a 1 when the input value is more than or equal to 1 and returns a 0 when the input value is less than 1. This can be used to differentiate between positive and negative values where required.

Counters

The Counter component in the DCS library counts from 0 to the specified maximum count value. The Current Count value increments by 1 each time the INC Count property is pulsed, up to the specified maximum count value. The counter stops at this maximum count value and will not continue the counter will again start counting at 0 whenever the counter is reset.

The Up Down Counter component in the DCS library counts automatically from 0 and increments the Current Count value by the specified Increment Size using the Time Step Size property of the Scheduler in the Solvers and Utilities library as the pulse to count. The counter can be configured to count up or down. A reset value specified the value that the counter will start counting if the counter is reset. There is no internal maximum or minimum count value that must be set. The counter can be used to keep time if the Increment Size is set equal to the Time Step Size property of the Scheduler in the Solvers and Utilities library.

I/O

The DCS DI in the DCS library is an external value used inside the control system. The DCS DI component imports this value to inside the control system. This can typically be a proximity variable in the plant environment.

The DCS DI & DO in the DCS library is a combination of the DCS DI and the DCS DO component.

The DCS DI List in the DCS library are external values used inside the control system. The DCS DI List component imports these values to inside the control system. These can typically be proximity variables in the plant environment.

The DCS DO in the DCS library is a control system internal value sent outside the control system. The DCS DO component exports this value to plant environment. This can typically be a on/off control to the plant environment.

The DCS DO List in the DCS library are control system internal values sent outside the control system. The DCS DO List component exports these values to the plant environment. These can typically be on/off controls to the plant environment.

The Digital Constant in the DCS library is an internal value used inside the control system. This can typically be an alarm indication defined inside the boundaries of the control system itself.

Logic

The AND gate is a logic gate that effectively finds the minimum between all of the Inputs. If any one of the inputs is a 0 the output will be 0. The OR gate is a logic gate that effectively finds the maximum between all of the Inputs. If any one of the inputs is a 1 the output will be 1. The XOR gate is short for exclusive OR. An XOR gate functions as a OR gate, finding the maximum, except where all the inputs are 1. For this situation the output is 0. The following sections provide explanations and tables for the specific AND, OR and XOR gates applicable.

 2 Input AND

The 2 Input AND component in the DCS library implements logic conjunction.

The 2 Input OR Gate component in the DCS library implements logic disjunction.

The 2 Input XOR Gate component in the DCS library implements exclusive disjunction

The 4 Input AND component in the DCS library implements logic conjunction.

The 4 Input OR Gate component in the DCS library implements logic disjunction.

The 4 Input XOR Gate component in the DCS library implements exclusive disjunction.

The 8 Input AND component in the DCS library implements logic conjunction.

The 8 Input OR Gate component in the DCS library implements logic disjunction.

The 8 Input XOR Gate component in the DCS library implements exclusive disjunction.

NOT gate

The NOT gate component in the DCS library implements logic negation. A NOT gate simply gives an output of 1 when the input is 0, and an output of 0 when the input is 1

Switches

The 2 of 3 Selector component in the DCS library returns a 1 if at least 2 of the 3 inputs are equal to 1, and returns a 0 for all other scenarios.

The 4 of 6 Selector component in the DCS library returns a 1 if at least 4 of the 6 inputs are equal to 1, and returns a 0 for all other scenarios.

The Digital Toggle Switch component in the DCS library allows the functionality to switch between the two inputs. The switch over from Input 1 to Input 2 and back is done by changing the Toggle property from 0 to 1 and back again. 

The Latch component in the DCS library is a simple Set-Reset Latch with the possibility to configure either Set (SR) or Reset (RS) as the dominant state. With both Set and Reset 0 the component is in storage mode and the output is kept at a constant state enabling the storage of one bit of information. The Set property sets the output value to 1 (with no invert set) and the Reset property resets the output to 0 (with no invert set). If the Set is dominant the reset can only happen if the Set is again 0. If the Reset property is dominant the set can only happen if the Reset is again 0. The Toggle property is used to set the output to the correct initial state.

Timers

Extended Pulse Timer

The Extended Pulse Timer component of the DCS library output value is 1 for the duration of the Preset Time following a positive edge of the SET property value.

The Off Delay Timer component of the DCS library will change its output value from 1 to 0 a specified time (Preset Time) after the SET property value is change from 1 to 0 and will remain 0 while the SET property is still 0.

The On Delay Timer component of the DCS library will change its output value from 0 to 1 a specified time (Preset Time) after the SET property value is change from a 0 to a 1 and will remain a 1 while the SET property is still 1.

The Pulse Timer component of the DCS library gives out a 1 for the duration of the Preset Time on a positive edge of the SET property value while the SET property remains 1. If the SET property drops to 0 before the reset Time is over the output value will also go to 0.

The Stored On Delay Timer component of the DCS library will change its output value from 0 to 1 a specified time (Preset Time) following a positive edge of the SET property value. The output value is stored as 1 and will only change back to 0 to restart the timer following another positive edge of the SET property value.

The Compound Execution Number component in the DCS library is used to add an Execution Number when creating a new compound component. A Compound Execution Number component must be placed on the sheet of the new compound component.

 

 

 

Controllers

The Advanced PID component in the DCS library uses a variation of the ideal PID controller structure. It uses the ideal form with a filtered derivative. The PID and Simple PID components both use the ideal parallel form.

 

 

 

The PID and Simple PID components in the DCS library both implement the ideal parallel form of a PID controller.

 

 

Simple PID

The PID and Simple PID components in the DCS library both implement the ideal parallel form of a PID controller. The Simple PID controller has less configured properties that the PID controller.

 

 

 

Filters

The Integrator component in the DCS library performs mathematical integration operation of signals with respect to time. The integrator provides as an output the summed area under the input signal.

 

 

 

The Rate Limiter component in the DCS library limits the rate at which the Rate Limiter’s output can increase or decrease when following the input value. If the output increase rate is more than the specified increase rate the Rate Limiter limits the increase rate to the specified increase rate. Similarly if the output decrease rate is more than the specified decrease rate the Rate Limiter limits the decrease rate to the specified decrease rate. The rate limiting is done by either a linear type specified in per second and the first order type specified in seconds.

 

 

 

The Rate of Change component in the DCS library performs mathematical derivation of signals with respect to time. The rate of change (derivative) provides as an output how much the input signal is changing at time t.

 

 

The Time Delay component in the DCS library delays the output signal from the input signal by the specified Delay Time. The input signal observed at the input port will only be observed at the output port the specified time later where is the specified Delay Time.

 

 

I/O

The Analog Const in the DCS library is an internal value used inside the control system. This can typically be a multiplication factor value defined inside the boundaries of the control system itself.

 

 

The DCS AI in the DCS library is an external value used inside the control system. The DCS AI component imports this value to inside the control system. This can typically be a measured variable in the plant environment.

 

 

 

The DCS AI & AO in the DCS library is a combination of the DCS AI and the DCS AO components.

 

 

 

The DCS AI List in the DCS library are external values used inside the control system. The DCS AI List component imports these values to inside the control system. These can typically be a measured variables in the plant environment.

 

 

The DCS AO in the DCS library is a control system internal value sent outside the control system. The DCS AO component exports this value to plant environment. This can typically be a controlled variableto the plant environment.

 

 

The DCS AO List in the DCS library are control system internal values sent outside the control system. The DCS AO List component exports these values to the plant environment. These can typically be controlled variables to the plant environment.

 

 

The Timestep component in the DCS library provides the Time Step Size specified in the Scheduler of the Solvers and utilities library.

 

Math

The 2, 4 and 8 Input Multiplier components in the DCS library performs a multiplication operation of the 2, 4 or 8 inputs provided at the input ports respectively. The result of the multiplication is provided at the output.

 

 

2, 4 and 8 Input Summation 

The 2, 4 and 8 Input Summation components in the DCS library performs an addition operation of the 2, 4 or 8 inputs provided at the input ports respectively. The result of the summation is provided at the output.

 

 

Absolute Value

The Absolute Value component in the DCS library provides at the output port the absolute value of the input value. The Absolute Value component basically provides a positive value at the output port of the positive or negative input signal. For a positive value the input and output signals are equal. For a negative input signal the output signal will be equal to the input signal multiplied by -1, resulting in a positive output signal.

 

 

Analog Select

The Analog Select component in the DCS library provides the option of selecting the Maximum, Minimum, Average, or Mean value, of the input values, at the output port. Any number of input values can be specified.

 

 

 

Clamp

The Clamp component in the DCS library limits the input value to a maximum and a minimum value. If the input value is more than the specified maximum limit the output value will simply equal the maximum limit. Similarly, if the input value is less than the specified minimum limit the output value will simply equal the minimum limit.

 

 

Divide

The Divide component in the DCS library performs a division operation of the 2 inputs provided at the input ports. The division done is given in Equation 2.34. The result of the division is provided at the output.

 

Function Generator

The Function Generator component in the DCS library allows the user to define output values corresponding to specified input values.

 

 

 

Modulus

The Modulus component in the DCS library breaks down the two specified inputs into a whole and a remainder or fraction value The Output property value is equal to the number of times that the input 1 divides into the input 2, and the Remain Output property value is then the remainder of this fraction.

 

 

 

Power

The Power component in the DCS library raises the specified input value to the power of the specified Power property.

 

 

 

Scale

The Scale component of the DCS library gives a output value that scales the input specified value by a Gain (Input A) and a Bias (Input B).

 

 

 

Statistics

The Statistics component in the DCS library provides the option of selecting the Average, Maximum, and Minimum of the input value at the output port. unlike the Analog Select component the Statistics component continuously samples and calculates the result from a single input value.

 

 

 

Subtract

The Subtract component in the DCS library performs a subtraction operation between the 2 inputs provided at the input ports. The result of the subtraction is provided at the output.

 

Waveform Generator

The Waveform Generator component in the DCS library provides the option of selecting a Sine wave, Saw tooth, Triangle, Square or Noise as the output signal. Additional properties that can be specified are the period of the wave, the amplitude of the signal, and the offset.

 

 

 

Weighted Average

The Weighted Average component in the DCS library calculates the weighted average of the two inputs according to the specified weights for each of the inputs.

 

 

Switches

The Analog Value Storage component in the DCS library stores the last input values for a specified time and on request provides these stored values at the output port.

 

 

Comparator

The Comparator component in the DCS library compares the 2 input values according to the selected switching type. The output value will be a 0 if the comparison criterion is false and a 1 if the comparison criterion is true.

 

 

Toggle Switch

The Toggle Switch component in the DCS library allows the functionality to switch between the two inputs. The switch over from Input 1 to Input 2 and back is done by changing the Toggle property from 0 to 1 and back again.

 

 

This case study demonstrates the control of a three stage chiller plant that cools water in a primary loop, which feeds into a secondary loop with a heat load.