User Solutions
(Issue 2, 2004)

Ever wonder how AutomationDirect
customers are applying their products?

--Check out some of the application stories we've collected and you'll see that AutomationDirect products are used in a wide variety of applications across many different industries. ---
Jump to Application Spotlight

D2-250 PLC PID loops control pumps in
residential water system

by Peter Carman,
Wyoming Controls
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We used PID loops in the D2-250 CPU to control three pumps and maintain pressure in a residential water system. The flow demand varies from zero to 250 gallons per minute. The pumps all have variable speed drives with the speed reference and run commands coming from the 250 CPU. At low flow, one pump runs alone, as needed, to maintain the pressure. As the flow increases, the other pumps are brought on, either in tandem with the first, or at a constant flow rate. The flow from each pump has an upper limit; if the total flow demand exceeds the combined upper limits, the pressure will fall. The result is that each pump can operate in an optimum range on its pump curve, and a widely varying flow can be delivered and the pressure is maintained very closely. The operator interface is a color touch screen
that displays the pump status, flow rates, and system pressure. All the setpoints for pump on/off and associated time delays are easily accessible to the system operator.

D2-250 CPU maintains water pressure for city water system

by John Neiswanger,
Industrial Electronics
___________________________________________________________________________

We created a water pressure controller for a local city water system. We used a pressure transducer to feed a water pressure signal into the DL205 PLC system analog card. The output from an analog card is used to vary the speed of a 75 HP well pump, controlled by a variable frequency drive, to keep the city water system at a more constant pressure. Setpoints are entered with a touch panel and the pressure is displayed as well. The system controls the startup sequence, releasing the well flow to a drain and slowly cutting into the system to prevent a pressure spike on startup. It also controls the shutdown to prevent a pressure dip. System pressure is maintained with a PID loop in the D2-250 processor.

DL06 PLC and EZTouch panel help move cement at bulk handling facility

by Jeff Bailey,
Ozinga Bros. Inc
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We recently installed a bulk cement handling facility. The facility offloads cement from river barges and pneumatically conveys the powder into a massive storage dome and truck loading facility. The concrete dome, which can hold 30 barge loads of cement powder, was erected using an inflatable air form system. A MODBUS network of four DL06 PLCs, controlled by an EZTouch Operator Interface, outloads the cement from the dome. A 4-20 ma PID loop implemented in one of the DL06 processors controls the speed of two hydraulically driven sweep augers. An analog radar sensor monitors the cement level in the truck-loading silo. All three primary functions are graphically animated and displayed on the EZTouch panel. The "supervisory master" DL06 controls the pneumatic conveying system and acts as the communications hub for the slave processors. Each processor runs local functions independent of the master. One feature that is particularly useful is the alarm history on the EZTouch panel. Future planned expansions of this facility will be simply and easily added to our system network.

Aluminum anodizing system controlled
with help from D2-260 PLC system and
EZText panel

by C R Williams,
Robo Systems
___________________________________________________________________________

Our system controls aluminum anodizing. The operator uses an EZText panel to enter the size of the job and the desired thickness of anodizing. The D2-260 translates this into the necessary current, voltage, and time profile required to produce the desired result, and controls a 300kW SCR switched power supply that delivers the anodizing current to the workpiece. Since the optimum waveform has both short term (~1sec) and long term (~5min) components, and needs precise control over two orders of magnitude (10A to 1000A), the floating point math capabilities of the D2-260 are used quite heavily. The environment is extremely noisy electrically (because of the 300kW SCR phase angle switching), so the design of the grounding and shielding, as well as software filtering, were very important to the success of the project.

In addition to the standard PLC on/off inputs and outputs, analog inputs and analog outputs are used as part of the monitoring and control process.

Cost-effective I/O simplifies hydroelectric
plant controls upgrade

by Lynn Mitchell,
Operations Superintendent
Lockhart Power Company

by Andy Feimser,
President
North Fork Electric
___________________________________________________________________________

Lockhart Power Company owns and operates a hydroelectric plant located on the Broad River in upstate South Carolina, and services over 6,000 direct customers and 6,000 indirect customers over its 90-mile transmission network. The plant includes an 8-gate dam feeding a canal that channels the water flow to the powerhouse, which contains five turbine generators with a combined power capacity of over 17 MW. The dam and turbine control system receives data from power, flow, and level sensing devices to perform monitoring and control of the dam, generators, and associated equipment.

The previous control system, installed in 1987, was a proprietary microprocessor-based system that had become obsolete. Lockhart required a control system that would provide open networking capabilities, and result in a lower total cost of ownership. The new system needed to coexist with an upgraded design of the existing hardwired generator controls, and perform distributed, independent control at the dam and each of the five turbine stations. Each I/O control node would replace the old equipment in the existing control cabinets and be networked to the central control room.

Systems integrator and vendor selection

Lockhart Power contracted North Fork Electric, a provider of hydroelectric products and systems integration services in Crumpler, NC, to lend their expertise to the renovation. North Fork Electric proposed a 3-tier solution. Level 1 included new hardwired controls for manual operation of the system. Level 2 included PLC-based control of the dam and generators in an automatic mode. Level 3 provided PC-based redundant control and monitoring from a central location, and also supplied connectivity to the plantwide Ethernet network.

System components

The system consists of seven DL205 micro-modular PLCs using D2-250 CPUs with built-in PID functionality. Each of the five systems for generator control includes analog I/O and an Ethernet communications module. The remaining two PLCs are configured in a master/slave arrangement and control the dam gates, located upriver from the powerhouse, via radio modems.

To reduce maintenance costs, North Fork Electric selected DL205 I/O components to maximize commonality among all systems. The identical analog output modules used on the generators, configured for ±10 VDC, can be configured for the 0-5 VDC dam gate control signals by simply moving the module's range selection jumpers. AC/DC relay modules are also used for both generator and dam control. Two operator interfaces and a Windows NT-based PC running the LookoutDirect SCADA/HMI software package complete the system.

System operation

In the automatic mode, the PLC can start, stop, and operate the generator via two PID loops that control startup and synchronization of the turbine. Changing the generator gate position varies the flow of water to the turbine, and thus the generator's speed/frequency. To bring a generator online, it must first be synchronized with the line frequency of the power utility. The first PID loop slowly increases the generator speed until it reaches 90% of the setpoint, at which point the logic switches to frequency control. Once online, the generator's power output is varied by changing gate position.

To complete Level 2 control, North Fork Electric then installed the dam control system. This system controls the eight canal gates located at the dam, which regulate the flow of water downstream to the turbines. The operator enters the required gate-position setpoints using a color touch panel connected to the dam control's master PLC in the control room. Data is transmitted to the slave PLC, located at the dam, via 900 MHz radio modems. The slave PLC monitors individual gate positions using proximity switches that count teeth on the drives' gears, and moves the gates up or down until they reach the desired positions.

North Fork Electric engineers then implemented the third and final tier of control and monitoring. The LookoutDirect SCADA system communicates to all the PLCs over an Ethernet network, performs supervisory control, and collects data that is easily passed to the plant's information system.

The installation was completed in four weeks to provide Lockhart Power with a powerful, yet simple, redundant control system that uses their familiar hardwired design as the manual control mode.
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