Monitoring Natural Gas Compressors - CDL Gateway™

The CDL Gateway™ is a pre-configured data aggregator and protocol converter that automatically determine what type of CAT® engine it is connected too and converts the Cat Data Link (CDL) into as many as 6 protocols simultaneously. Very little, if any, setup is required in the field because the CDL side is automatic and the output side is pre-configured according to the customer's needs. Setup in the field is normally limited to setting device addresses for serial networks or IP addresses in Ethernet applications using our free software, MonicoView™. Therefore, installation cost is dramatically reduced and integration time is minimal.

The most common application for the CDL Gateway™ is for monitoring Natural Gas Compressors used in Midstream Gathering and Pipelines. The majority of compressors are Natural Gas fueled reciprocating engines driving reciprocating compressors. The largest market share for engines is held by Caterpillar® and the largest market share for reciprocating compressors is held by Ariel. The CDL Gateway™ not only has the ability to monitor the Caterpillar® ADEM II and ADEM III engines directly without need for intermediary devices, but can also act as a Modbus Master to gather data from the Compressor controller. The most common non-PLC compressor controllers are from Altronics and FW Murphy. The CDL Gateway™ commonly acts as a Modbus master to the FW Murphy Centurion or Millennium products as well as to the DE-2500 and DE-3000 products from Altronics. The most common PLC based compressor controllers are from Allen Bradley, GE Fanuc, and Siemens. The CDL Gateway™ has the unique ability to establish two-way communications with all of these brands, without any need of special drivers or modules, which allows for some very powerful communications and monitoring networks. One of the more exciting applications is the FW Murphy Centurion PLUS, which uses the CDL Gateway color touch screen HMI as the primary operator interface for the compressor system.

The basic CDL Gateway™ has the ability to integrate all of these devices and then provide a consolidated interface to a SCADA system. A common example would be where the CDL Gateway™ gathers information from the engine and the Compressor controller and provides all this information as a unified Modbus Slave to the SCADA system. Many times we will integrate a station-level PLC into the mix as well. In this case, we will provide engine and compressor data to the PLC and also pull station data from the PLC and provide a unified interface to the SCADA system. One benefit of this architecture is significantly increased speed due to the elimination of two devices over the largely serial networks.

The CDL Gateway PLUS™ adds many benefits, but one of the most valuable is real-time data logging. Since the Gateway is primarily a Data Concentrator, the data logging feature offers the ability to log real-time data from all connected devices for detailed forensic analysis. Most serial SCADA networks cannot provide real-time data collection because of network limitations due to the number of devices. An average serial SCADA system for a large gathering operation only polls each device every 2-15 minutes and a lot can happen inside that window. Therefore, SCADA is best suited for long-term trending, but real-time data logging can provide valuable data to analyze failures. Many of our customers are able to pull log files that simultaneously log engine data, compressor data, and station data such as suction pressures in one integrated file for maximum analytic capability.

One customer's SCADA system was only able to poll each compressor every 2-3 minutes, but was experiencing cylinder liner failures on two engines every 1-2 weeks. The data from the SCADA system was not showing any possible cause and at $14,000 per repair, it was causing a lot of pain. The CDL Gateway PLUS™ was installed to gather data from the engine and the acted as a Modbus master to an Altronics DE-2500. A log file was created to record 20 compressor parameters and 60 engine parameters every three seconds. Each CSV file contained one day of data and 200 daily files were contained in a FIFO file on the 2 GB Compact Flash card. With this real-time data, the customer was able to see the coolant temperature spikes that were causing the eventual failures. This customer then installed CDL Gateway PLUS™ units on all Compressors in their 100+ engine fleet.

The only limitation of the CDL Gateway™ is the number of ports. It offers (2) RS-232 ports, one RS-485 port, and one Ethernet port in addition to the proprietary CDL Gateway� Port. Each serial port can communicate using one protocol, either master or slave. The Ethernet port can communicate using four protocols simultaneously. The serial port can be used to gather data from other devices such as flow meters, compressor controllers, pyrometers, and many legacy PLC's. The Ethernet port can be used to provide data integration between different PLC's. For example, if you want to integrate an Allen Bradley SLC 5/05 with a ControlLogix, it is very simple. If you need to integrate these two Allen Bradleys with a GE Fanuc 90/30 and a Siemens S7-315, it is also very simple.

• The CDL Gateway PLUS™ also adds IP features such as:
• Email notification upon alarm using the SMTP Server
• Sync server to sync log files to a remote server over TCP/IP
• FTP server to allow remote access to the log files from a remote FTP Master over TCP/IP
• Virtual color touch screen HMI over Internet Explorer
• Custom HTML web Server for customized web integration

• The CDL Gateway™ also allows for the addition of Input/Output Modules such as:
• Thermocouple Inputs for individual cylinder temps, bearing and winding temperatures, or Pre and Post Catalyst temperature sensors
• RTD Inputs for bearing and winding temperatures
• Analog Current inputs for pressure sensors or continuous fuel tank sensors
• Digital SSR inputs and outputs for digital information such as fuel tank sensors and switchgear relay status.