Control Engineering

Some time ago we promised to reveal our technically preferred tested vendors for the Phase I portion of this project, when this was being considered by the City. The contract was awarded some months back to a long established supplier of dedicated pump controllers (which have served the City well for the past 10 years). So a good reputation ruled.

The technical review was given birth by the fact that the City's present RTU/HMI contract had expired. That contract was based upon Modbus as a communication standard, using a Modbus controller, HMI and Modbus cell modems. It became apparent in our meeting with the prime consultant that Ethernet had become the preferred protocol, and direct Ethernet cell modems had recently become available for the same cost as the Modbus units.

Therefore, in our technical review we considered alternative architectures employing Ethernet HMIs and controllers with a direct Ethernet cell radio. We considered solutions available in the same price range as the RTU and HMI that was to be provided on the previous (expired) contract. We tested the most promising alternative. The tested alternative also included a cost-effective 0-55 degree C Ethernet switch/router/firewall.

Our tested combination of vendors were:

• RTU: Wago 750 Series Ethernet controller with IEC1131 programming software
• HMI: Advantech TPC-60S WinCE 6" color touchscreen with Indusoft WinCE Web Studio 150 tag run time.

We considered various configurations from the leading U.S. PLC vendors, however the solutions they can offer in this price range don't come close to the functionality of the tested combination. Using the leading vendor's Ethernet increases our Phase III SCADA costs, as they only support EtherNet/IP protocol, which means we need to add additional OPC server drivers to accommodate them (Wago supports both Modbus TCP and EtherNet/IP; the provided Modbus OPC server also supports Modbus TCP).

While Wago is better known for terminal blocks than I/O and controllers, they have been in the I/O business for 10 years and the controller business for 5 years. Their IEC1131 software is as capable as a $3,000-5,000 package from the leading U.S. PLC vendors, yet the cost is less than $1,000 for an unlimited City site license (no keys).

Wago can do this because they and 70 other vendors share the same programming software (to my knowledge, this alliance of 70 vendors using the same programming software is the only example that

IEC1131 has of vendor independence). They have been in business more than 50 years and are between $.5B and $1B in sales - not as big as the leading PLC vendor, but much bigger and stronger than the proprietary pump control and SCADA RTU vendors selected by the City.

Advantech is a widely used OEM to the U.S. electrical industry. They are among the world's largest suppliers of industrial PCs, 1,000 employees, 20+ years in business, more than 400 PC-based products. The leading water process equipment manufacturer in the U.S. brand labels their PC hardware. There are a dozen or more vendors of similar hardware that could be substituted and still run the same software, making this a truly vendor independent HMI solution.

Let's review the specs
So you don't have to page back through all the blog entries since last fall, here again is the capabilities outline that drove our choice:

The capabilities of the tested architecture/hardware/software (not specifically mentioned in the original spec but desirable) include:

1. Elimination of most relays and all analog isolators:

A. Digital I/O is individual isolated (necessary to work with separate CPTs in motor starters and VFDs unless relays are added) B. Analog inputs (differential) are optically isolated so that station 4-wire drive speed feedback and flow inputs stay isolated from one another C. Analog outputs are optically isolated so drive speed reference outputs stay isolated from one another D. The 2-wire analog input (differential) from bubbler pressure transmitter powered by panel 24VDC power supply, is isolated from all 4-wire inputs

2. Centralized configuration management for the RTU and HMI. (City has had definite problems with this in past). Easy for maintenance personnel to maintain the system.

A. RTU and HMI can be reprogrammed over the cell network from one of the SCADA servers (by QDS Systems or the City using remote terminal server admin, from any authorized Internet-connected computer) B. RTU and HMI have common IP addresses at all sites; only the modem address varies. Router/firewall/switch has common configuration at all sites. This is important in that it allows any of these parts to be changed without needing to get out a notebook computer to set an IP address (i.e. they need only one spare of each type of device and we pre-configure all the spares with the default IP address). Because Verizon takes awhile to setup cell accounts, a spare modem and Verizon account is recommended.

If a modem needs to be changed, the City can change the modem, call us and we will (from our desktop while they are on the phone) change the IP address in the OPC servers to point to the new modem's IP address.

C. HMI contains configuration of RTU. To replace an RTU controller head, replace head (5 minutes) and push download button on HMI (password protectable). We can also, from our desktops, download to the RTU from the central server.

D. HMI application resides on a compact flash card. To change out an HMI, replace unit (5 minutes) and move compact flash card to new unit. If flash card has been corrupted, use supplied backup flash card. We can also, from our desktops, download to an HMI from the central server.

E. Setpoint changes have often been lost when controllers are replaced.

This can be virtually eliminated by the HMI automatically updating its copy of the RTU program on a daily basis, including setpoints. To ensure central configuration stays current without incurring excessive cell traffic, we recommend that RTU configurations be transmitted from the local HMIs to the central server on a monthly basis.

F. HMI has the same look and feel as the central HMI, reducing the operator and maintenance personnel learning curve.