2396

Understanding Modbus RS-232 and Modbus RS-485

Table of Contents:

(see left menu for scrollable page)

  1. Overview
  2. Using Modbus for Legacy Gear
  3. The Modbus Protocol
  4. Serial-to-IP Modbus Bridge
  5. Modbus Master/Slave, Registers, & Coils
  6. Remote Monitoring and Control with Modbus
  7. SNMP-Modbus Protocol Converter
  8. Track Generator Output with Modbus
  9. Connect Modbus Controllers to Your SNMP Manager
  10. Central Alarm Aggregation For MODBUS, TL1, and...

Overview

Brief Overview of Modbus RS-232 & Modbus RS-485 in Remote Alarm Monitoring.

Modbus Remote Monitoring and Control traditionally uses RS-485 and RS-232 transport for collecting data from Modbus slaves using established protocols. Of the two, Modbus RS-485 is more common than RS-232 due to its support for multi-drop communication.

Modbus is a protocol that (traditionally) uses serial communication lines. These serial lines connect the master to Modbus slave devices for collecting register and coil information. Modbus/TCP was introduced for LAN installations but Modbus over traditional serial networks is still found in many industrial applications. A Modbus master can communicate with up to 247 Modbus Remote Telemetry Units (RTUs) or Intelligent Electronic Devices (IEDs). It uses a unique Modbus address assigned to each RTU.

Modbus is just one possible protocol that can be sent via dedicated serial connection.

These transports are not in any way limited to Modbus, and are found in a wide variety of other applications.


Differences between Modbus RS-232 and Modbus RS-485 Capabilities.

Modbus RS-232 Allows Concurrent, Two-Way Flow of Data

Modbus via RS-232 sends data in the form of time-series of bits. It is a standard for communication between data terminal and data circuit termination equipment. Transmission (Tx) and receipt (Rx) for data occurs on different circuits when using Modbus RS-232 lines. That means that data is able to flow both ways at the same time.

Modbus RS-485 Indicates Values Using Differences in Voltage

RS-485 is similar, but distinct, from RS-232. This two-wire, multipoint connection communicates data by indicating values by sending different voltages across the two wires. These differences between these voltages are related to one and zero values, which make up the Modbus RS-485 communications.




Legacy Gear: Using Modbus to Monitor a Generator Controller in Your Network:

Several DPS clients use Generac, Caterpillar, Kohler, and other generators. They wanted us to interface RS232 / RS485 serial Modbus to the generator controller. Also possible is to use DPS D-Wire propane monitoring sensors to report back to a NetGuardian RTU.

Modbus for remote monitoring and data acquisition of client-premise devices:

Another client needed remote monitoring and data acquisition for devices they sell to their customers. Their primary business is measuring liquid in tanks (refineries, petrochemical plants, etc.). They have digital inputs (magnetic switches) in their existing management system.

For decades, their customers have put a mechanical device on the tank. The problem is that wiring is expensive to install and maintain. Over the years, they've installed several radio systems, but the radios are typically 900mhz/2.4ghz spread spectrum.With GSM reporting from a modern monitoring device, the options multiplied.

We could enable customers to get the data not just in their own office, but also from almost anywhere else in the world.

The tank sensors themselves are analog. There is some intelligence in the enclosure that converts analog to Modbus RS485 or RS232. This client came to DPS looking for one small, GSM-capable, and inexpensive device on each tank. They would also need a central collector of some kind (T/Mon).

As you can see, Modbus projects tend to involve a lot of other protocols and equipment.


Working with Modbus in an increasingly IP & SNMP driven world.

If you work in telecom, you probably have trouble with any remote RS485 Modbus equipment. The world has shifted more and more to IP, T1, fiber, and other modern transport standards. Dedicated serial lines are tough (and expensive!) to maintain. Wouldn't it be nice to route serial traffic over IP? Then you could keep you old-but-still-functional Modbus gear but abandon the aging serial transport.

One excellent new solution to this problem is a remote Modbus-to-SNMP mediator.

This is a fairly simple box that takes in serial Modbus (RS-232 or RS-485) and converts the message to standard SNMP traps. These can be received by your SNMP manager. Because the mediator box is modern, you benefit from recent innovations like SNMPv3. Unlike earlier versions of SNMP, SNMPv3 is secured with encryption. For many organizations, this is level of security is needed whenever data will be sent via IP.

If serial transport isn't your problem, but you still want to integrate Modbus into your SNMP umbrella, you can take a different route. This involves using a Modbus mediating master station to convert inbound Modbus to SNMP. This single stream of usable SNMP traps can be easily sent to your preferred SNMP manager. This master-station solution will generally be much less expensive than installing individual mediation devices at each of your remote sites.




The Modbus Protocol

In this Real-World Example, we see the fairly simple steps required to Track Your Generator Status and start polling data from a backup generator (propane/diesel). This example uses the web interface of the NetGuardian DINremote monitoring device.

Modbus is an open serial communications protocol. It was developed in 1979 for use with Programmable Logic Controller (PLC) devices, and is now widely used for connecting many types of industrial electronic devices connected on different types of networks.

Modbus is a Widely Used Protocol

Modbus is used extensively for a number of reasons, including the following:
  • Modbus is an open-source protocol, meaning that it can be included in a wide range of device types from any equipment vendor
  • Modbus uses a simple message structure, making it less difficult to deploy. Modbus might require just a matter of days to implement, a big improvement over the months of work that might be required to learn and deploy other protocols
  • Modbus moves raw words and bits, and it has very few restrictions

Modbus Utilizes Serial or Ethernet Connections

The Modbus protocol can be used with two types of serial connections, both RS-232 and RS-485. Some versions of Modbus can also be sent over Ethernet or TCP/IP. These Modbus communications are packed as a single bit, or 16-bit word packets.

Modbus is not part of a physical layer on a network, as with some other protocols. Modbus communications are transferred on top of physical layers, enabling it to be utilized on many different types of networks. This non-physical layer property makes Modbus an application layer protocol.

Two Variants of the Modbus Protocol

There are two variants of the Modbus protocol that travel over serial connections: The Modbus RTU and the Modbus ASCII.

Modbus RTU

This variation is more compact, and uses binary communication. In this format, data transmissions are always followed by a cyclic redundancy check checksum, which are used to detect transmission problems.

Modbus ASCII

This version is more verbose, and it uses hexadecimal ASCII encoding of data that can be read by human operators. A different type of checksum, the longitudinal redundancy check checksum, takes place after Modbus ASCII data transmissions. Modbus ASCII is the less secure of the two variants.
As it is also less efficient than Modbus RTU, operators should only utilize Modbus ASCII for the transmission of data to devices which do not support the Modbus RTU format. Modbus ASCII can also be useful when RTU messaging cannot be properly applied.

Modbus is a "Master/Slave" Protocol

Modbus communications take place between a centralized master and up to 247 connected electronic devices on a single network.

The design is commonly referred to as a "master/slave" protocol, because the system "master" requests information from connected devices, which are referred to as "slaves".

Slave devices only send information to the master in response to these requests, and do not operate autonomously. The master can also write information to the slave devices, but the slave devices cannot write information to the master.

When a slave device transmits a communication to the Modbus master, it begins the message with a unique address identifier. This is a number ranging from 1 to 247. This enables the master to identify which specific device is responding with the requested information.




Serial-to-IP Modbus Bridge

The Modbus Bridge allows Modbus Networks to work on a lot of types of networks. A Modbus bridge is a device that connects Modbus serial products to Modbus TCP Masters. It can be an important part of a Modbus network.

Modbus Bridge Allows Communication Between Modbus Serial and TCP Devices.

Modbus serial is the original variant of Modbus that travels over a serial connection. This serial connection commonly uses a RS-232 or RS-485 serial interface. Modbus TCP is an extra variant of the Modbus protocol. Internet users can access Modbus TCP at port 502, which is reserved for Modbus users on the TCP/IP stack.

Today, Modbus TCP has become an popular variant of the Modbus protocol. A Modbus bridge will allow users to transition to this variant, while still making use of their Modbus serial gear.

A Modbus bridge may be configured as a Slave or a Master bridge, simply by connecting to either device serially. A Modbus bridge can also be used for other Modbus variants, such as Modbus ASCII and Modbus RTU.

Connect 1000s of Slaves With Just a Single Modbus Bridge.

With a Modbus bridge, users can connect thousands of slave devices using a single Ethernet card and the Modbus TCP protocol. Devices joined to a Modbus bridge have single IP addresses, and addressing slaves through the Modbus bridge is now defined by the IP address and the slave address or unit id.

When a Modbus bridge receives a Modbus TCP request, it converts the messages into Modbus RTU or other variant of the Modbus protocol, creating a response using Modbus TCP.

In these cases, the Modbus master most likely does not even see that it is not actually communicating with a Modbus TCP device.

Modbus Bridge Can Connect to Many Modbus TCP Masters at Once.

A Modbus bridge can connect to many Modbus TCP masters at one time. Serial slaves will actually see the Modbus bridge as the master device. The actual TCP Modbus masters will treat the Modbus bridge like a group of slaves, communicating as if each single master had sole access to the slave devices. With more masters accessing the Modbus bridge, response times can become slightly sluggish.




Modbus Master/Slave, Registers, & Coils

Modbus is a protocol used for machine-to-machine communication in a wide variety of industrial applications. The communcation occurs over some kind of network transport. Modbus is generally used for Remote Monitoring and Control where data is collected from and commands are issued to instrumentation and control devices.

Modbus Uses a Master/Slave Model

In Modbus networks, there is typcially one master and multiple slave units. Modbus masters will either request information from or issue commands to Remote Telemetry Units (RTUs).

Each RTU is assigned a unique Modbus address to enable data and commands to be routed correctly over a network. Traditionally a Modbus network was a multi-drop serial channel like RS-485 or RS-232 with appropriate unit isolation. In these traditional networks, up to 247 RTUs could be connected at one time.

Modbus/TCP was introduced to take advantage of contemporary LAN infrastructure. Modbus/TCP increases the number of units that can be connected to the same network.

Modbus Data is Exchanged in the Form of Registers and Coils

Data is organized in 16-bit registers with commands available to access an entire register or in some cases individual bits. Writing to a coil or register generally represents controlling the Remote Telemetry Unit or something it's connected to. Each RTU manufacturer has considerable freedom in determining what each register means for its telemetry. A Modbus register map is typically available to enable master configuration.

An Advanced Modbus Master Can Support Your Other Protocols

MOM

An advanced Modbus master can be used for more than simply communicating with Modbus slave devices. When seeking a master for your Modbus network and other devices, you should look for a master than can bring your Modbus alarms and notifications from your other protocol devices into one master screen. This will help you monitor your network as efficiently as possible, eliminating the need for multiple operators and workstations to accomplish your network alarm monitoring.

T/Mon NOC is an Advanced Modbus Master that Saves Your Company Money

The T/Mon NOC is one such Modbus master that can greatly increase your organization's visibility while reducing your monitoring costs.

With an ordinary Modbus master, you will be unable to collect alarms from your non-Modbus devices.

This will require you to deploy multiple masters to support all of the different protocols within your network, and hire additional operators to monitor the communications from these assorted masters.

With T/Mon NOC, you can have Modbus alarms and alarms from over twenty-five additional protocols forwarded into one master browser. This convenient, single-window view allows you to monitor your entire network of devices through a single workstation, using a single operator.

T/Mon NOC Modbus Master Sends You Page and Email Alarm Notifications, No Matter Where You Are

Another advanced feature of the T/Mon NOC Modbus master is the page and email alarm notifications utilized by the system. Anytime an alarm occurs within your network, your Modbus master will send a page or email directly to your network technician. These pages can even be directed to specific technicians according to your technical staff's schedule, and their individual skill sets.

With these advanced features, you'll be the first to know anytime a slave device has lost communication with your Modbus master.



Remote Monitoring and Control with Modbus

Modbus is an open source protocol, which led to the widespread deployment of Modbus systems which are most frequently used for industrial applications. Multiple Remote Telemetry Units (RTUs) and/or Intelligent Electronic Devices (IEDs) that supports the Modbus protocol can be connected to the same physical network to create a Modbus network. A Modbus network, at its most basic, is a network of master and slave devices that communicate using the Modbus protocol. These Modbus networks typically utilize a serial connection while Modbus TCP/IP networks, which is made up of devices that supports the Modbus TCP/IP protocol, will usually use 10BaseT or faster for their connection.

A Modbus Network Can Support Many Slave Devices...

A common Modbus network consists of having a single master and multiple slave RTUs and/or IEDs.

The master/slave address design of a Modbus network enables a Modbus master to communicate with a specific device by using its unique Modbus address. This unique identifier, the address, has a range of 1 to 247 and can be located at the beginning of the message that will be sent to the Modbus master.

A simple Modbus network can have up to 247 connected at one time the same network. Each of the 247 connected Modbus devices are assigned their own unique identifier which they will use to communicate with other Modbus devices.

Note: Modbus TCP/IP networks can generally support more devices than a traditional Modbus serial network.

In a master and slave configuration, the communication stream is controlled by the Modbus master. The Modbus master can request data from or write data to Modbus slave devices across the network using specific register and/or coil addresses. The Modbus slaves on the other-hand can only respond to the master's requests or commands as it is received.

Multiple Modbus Variations...

The Modbus protocol has evolved into several different variations. These variations are designed to support Modbus network communications over a variety of physical network layers. These variations include Modbus RS-232 and Modbus RS-485, which will support different types of serial connections.

There is another variation of the Modbus protocol called Modbus TCP/IP.

The Modbus TCP/IP specification was created in response to the expanding usage of Ethernet. Since TCP/IP is the transport protocol of the Internet, Modbus TCP/IP, which is simply the Modbus wrapped with TCP/IP, can be used to communicate over a Modbus network structured with an IP connection.

Modbus TCP/IP provides a huge set of capabillties because of its compatibility with other TCP/IP support devices and software.

For example, a Modbus TCP/IP device that is located halfway across the world in a remote location can be still accessed through the Internet because of TCP/IP.

Two additional variants of the Modbus protocol are Modbus ASCII and Modbus RTU. These variations are optimized for use with ASCII equipment and with Modbus capable RTUs. Each of the aforementioned Modbus variants uses a slightly different communication format, allowing users to deploy a Modbus network in the variant that is the most compatible with their other equipment.

And Advanced Technology For Your Modbus Network.

A Modbus network should be developed using the most advanced Modbus monitoring technology. With advanced Modbus monitoring systems, you can provide automatic page and email notifications of all your alarms. With location and repair information sent directly to your technicians, you can handle network problems more quickly and efficiently. The most advanced systems will also allow you to bring in alarms from other protocols and can display all of your important notifications in a single window that can be monitored by a single network operator.

A master system such as the T/Mon NOC can be what you need for your Modbus network. It is a multifunction and multiprotocol system that provides a multitude of features all in a single-platform.

Modbus, SNMP, and ASCII are just a few of the many protocols supported by the T/Mon NOC. The T/Mon NOC comes with T/Mon GFX which is a graphically user interface for displaying alarms visually on a layered geographical map. Built to be the solution for a wide range of problems, it could be exaclt what you need.

Modbus Variants Supported by T/Mon NOC.

  • Any Modbus ASCII device.
  • Any Modbus RTU device.
  • Any Modbus TCP/IP device.

Definitions

Modbus

Modbus is a protocol developed in 1979 by Modicon for use with their Programmable Logic Controller (PLC). It is a free and open protocol which helped get the protocol adopted by many users and devices.

Serial Connection

A serial connection, or a serial communication, is the process of sending data one bit at a time over a connection or communication channel in a sequence.

10BaseT

10BaseT is a twisted-pair cable that is used for LAN and can achieve speeds of up 10Mbps.

RTU

A Remote Telemetry Unit (RTU) is a device created for monitoring and reporting events that occurs at a remote site. The typical events that will be monitored are temperature, humidity, and voltage levels. Almost anything can be monitored with an RTU. Information regarding these events are collected by the RTU and then sent out to a master station like the T/Mon.

IED

An Intelligent Electronic Device (IED) is a microprocessor-based controller that has advanced local control intelligence.

TCP/IP

TCP/IP is used as the transport protocol of the Internet and is made up of two different protocol layers. The first layer, the transport layer, called the Transmission Control Protocol (TCP) is used to break up a message or file into smaller pieces of data called packets that are then sent over the Internet. It is also responsible for rearranging the packets when it receives them. The second layer, the Internet layer, called the Internet Protocol (IP) is used for addressing the packets so that the packets will get to the correct destination.





The Right SNMP Modbus Protocol Converter

Modbus is an open protocol, meaning it does not belong to one company and can be used by any company. It was developed in 1979 for use with Programmable Logic Controller (PLC) devices, and is now widely used for connecting many types of industrial electronic devices connected on different types of networks.

Modbus is used extensively for a number of reasons, including the following:

  • Modbus is an open-source protocol, meaning that it can be included in a wide range of device types from any equipment vendor.
  • Modbus utilizes a simple message structure, making it very easy to deploy. Modbus might require just a matter of days to implement. This is a vast improvement over the months of work that might be required to learn and deploy other protocols.
  • Modbus moves raw words and bits, and it has very few restrictions.
Modbus is described as using a Master/Slave model. This merely means that there is typically one master unit that sends commands and receives data from one or more "slave" units.

The slave units are typically at remote sites and report COS to the master, which is at the central office. This allows for visibility of many sites without sending a tech to each site daily.

An advanced Modbus master can be used for more than simply communicating with Modbus slave devices. When seeking a master for your Modbus network and other devices, you should look for a master than can bring your Modbus alarms and notifications from your other protocol devices into one master screen. This will help you monitor your network as efficiently as possible, eliminating the need for multiple operators and workstations to accomplish your network alarm monitoring.

Modbus Protocol Converter (MPC) complements a Modbus Gateway

A MPC, such as an advanced modbus master, is a device that converts Modbus communications into other protocols, such as Simple Network Management Protocol (SNMP). In doing so, the MPC translates the data into a form that can be read by another protocol manager. This device performs functions similar to a Modbus gateway.

MPC Allows Use of Existing System Master.

Deploying a MPC at a network site will allow you to transfer your communications to the system master you are already familiar with. Because your Modbus alarms will be converted into another protocol, the master can treat Modbus alarms as any other alarm along a network.

Get Rid of the Need for Extra Operators with a MPC.

Using a Modbus protocol converter eliminates the need for a separate Modbus workstation or system operator. By converting your Modbus alarms to SNMP, you will be able to use your SNMP master as the master for your entire network of devices. All of your alarms come into a single browser screen. You will be able to use a single system operator to respond to alarms and dispatch techs.

The DPS T/Mon SLIM can be used as an advanced Modbus protocol converter. By installing the Modbus software module onto the SLIM, you will be able to view your Modbus alarms using your SNMP manager.

T/Mon SLIM is a Powerful MPC.

The T/MON SLIM is small, powerful SNMP Modbus master. With its compact size, T/Mon SLIM requires only one unit of space on your gear rack. While being scaled for maximizing your rack space, T/Mon SLIM is still able to provide the capacity you need to covert alarms from several Modbus devices. Additionally, it is compatible with other protocols as well.

You can monitor and mediate all your mission-critical gear with just one master.

If you are looking to mediate your Modbus to SNMP or other protocol within your network, you need an advanced MPC. With the T/Mon SLIM, you can convert your Modbus alarms to SNMP, ASCII, and several other protocols. Other benefits of the T/MON SLIM include monitoring switches and other equipment, monitoring up to 10,000 alarm points, receiving alarm notifications via SMS message, email and page, alarm history logs, nuisance alarm filtering and more.

To see extra info on a MPC, please visit the Modbus Gateway page.




Track Generator Output with Modbus

Generators are a critical part of any robust telecom network design. They are typically third rung in the power ladder. Commercial power is the primary source for normal operation, followed by your battery plant for short to medium term protection and generators for longer term operation without the primary commercial power.

Generators come in all sizes, shapes, power outputs, but they also vary widely with respect to the technology they use to report alarms.

Older generation equipment as well as basic models use relays to generate contact closures to report alarms. These types of generators require an RTU (such as the DPS NetGuardian 832A) to collect these contact closure, to report them back to an SNMP alarm master or make them viewable from a web browser. Newer equipment use higher level protocols, typically SNMP to provide more detailed status and alarm information. These alarms could report to your existing SNMP alarm master or a DPS T/Mon NOC. Newer generators may also come with their own administration / management tool. If it does, from a best practices point of view, you should consider this as an element manager layer. As such you should still have alarms forwarded to your NOC or MOM so you have generator visibility as part of your overall network view.


1. Generator Running

Take Care of Your Generators

Will report whenever the generator is running. Why is this alarm important? If the generator is running, chances are very good you have a commercial power failure. Most companies and NOC managers have experienced a network outage because nobody knew the generator was running, until it ran out of fuel, causing power failure. The end result, was the site still went down, the only difference is that it went down later and consumed lots of fuel. Under normal circumstances, this alarm would be used to make sure your self tests (manual / automatic) are working correctly.

It can also be used as a rough indicator of how long the generator had been running so you can estimate fuel levels and better plan fuel runs.

Lastly, whenever an unplanned generator running alarms occurs, it gives you plenty of time to initiate the corrective action notifications to the commercial power company.

2. Low Fuel

Low Fuel

Most modern generators give you the ability to observe fuel tank levels. However the Low Fuel alarm is the lowest common denominator with respect to fuel levels. When the generator senses that it has low fuel, it will report this alarm.

Generally when you see these alarms, you want to act real fast.
Depending on your windshield time to your site, and your low threshold warning level, it might already be too late to avoid down time. In cases where you have seasonal site access or have to fly in fuel, you have to have a very high level of fuel level awareness.


3. Oil Pressure

No Oil

Alarms when the oil pressure is low. Machine 101 - Oil protects moving parts. No oil - you will have a generator that will have some very expensive
repairs, or generator that is shut off that takes down your site. Collectively using these alarm elements allows you to:

  • Avoid / reduce the effect of site power failures.
  • Intelligently let you plan Truck rolls for service & fuel.
  • Manage your sites more efficiently and effectively during natural disasters where you have lots of outages and not enough manpower.
  • Save money on fuel, by avoiding waste.
  • Insure your generators are running properly, so they are there for you when you need them. (Confirm the self tests are running)

How to Monitor Generator Alarms

Monitor Generator Alarms, Battery Alarms, Intrusion Alarms, and High/Low Fuel Alarms
Monitor Generator Alarms, Battery Alarms, Intrusion Alarms, and High/Low Fueld Alarms.

How This Application Works:

Equipment Used.

  • NetGuardian 832A G4.
  • High/Low Fuel Sensors.
  • Intrusion Sensors.
  • Battery Sensors.
  • Generator Sensors.

The application features a NetGuardian 832A G4 along with the 19" Wire Wrap Back Panel and the 19" Pluggable Back Panel as options. This version of the NetGuardian G4 will support wide range on each of the power inputs (-24VDC & - 48VDC), giving you dual wide range power inputs.

This version of the NetGuardian 832A G4 comes equipped with 32 discretes, 8 analogs, 8 controls and the ability to ping 32 network elements. There are some minor hardware and software changes between the NetGuardian G2 and NetGuardian G4.

The NetGuardian G4 will be the perfect solution to monitoring your generator, battery, intrusion and low/high fuel alarms at your remote locations and reporting those alarms as an email message to your PC. With the built-in web browser, you will be able to view those alarms at any time, giving you 24/7 visibility to your remote site.

Click Here to Learn More about UPS Battery Backup Monitoring.


Use MODBUS to monitor your generator Output

How This Application Works:

Equipment Used:

Both of these applications will allow the T/Mon NOC to receive the alarm messages, whether it is the MODBUS protocol or the DCPx protocol. It turns those into alarm messages and sends them to your techs via e e-mail, text message or viewed via the web browser. The first option features the MODBUS Interrogator Software Module that will load onto your T/Mon NOC. This solution enables your T/Mon NOC to accept discrete and analog alarms from multiple MODBUS devices, including your generator. The T/Mon NOC will turn the alarm info into alarm messages and report to your techs.

The second option consists of the NetDog 82IP. This solution will monitor your generator's contact closures (discretes) and analog voltage values. It will report those as DCPx traps via LAN to your T/Mon NOC.

Installation of the NetDog 82IP will be a breeze with its built-in barrier strip in front of the unit and the included external temperature sensor will enable you to monitor the ambient temperature up to 7 feet away.

Monitoring Propane

Propare Monitoring

Propane generators are a common backup power source at a variety of sites. These technologies support monitoring of tank levels, flow rates, run times, and intelligent estimation of remaining run-time.

Sub-Technologies:

  • Propane Flow Rate Monitoring
  • Propane Tank Level Monitoring
  • Accumulated Run Timer
  • Estimated Remaining Run Time Calculation
  • RAM Buffering (for Storing PBX Data)

Products featuring Propane Monitoring:




Connect Your Modbus Controllers To Your SNMP Manager With This Mediator RTU


You probably have both Modbus and SNMP

In your network, you may have some Modbus controllers at remote locations. Many propane/diesel generators today utilize Modbus controllers, so consider them as one example of Modbus gear.

Generator controllers are a common Modbus example

You know that your remote-site generators are priceless. They kick on when power is out and your battery plant is running out of juice. If your generator fails, it won't be long before your site goes dark. Your customers will be upset. Your boss will be upset.

Modbus Diagram
In this diagram, your Modbus gear connects to the TempDefender G2. The TempDefender G2 mediates the Modbus to SNMP and sends it via LAN to your SNMP manager.

Modbus and SNMP aren't naturally compatible

Good remote monitoring of your generators is the obvious answer, but there are challenges. Some of your generators may not have SNMP capability or LAN access. They do a fine job of generating electricity, but they likely use a Modbus based controller. In today's SNMP world, there hasn't been an easy way to interface your Modbus controllers to your primary SNMP manager.

You need this simple conversion RTU

What you need is a simple device that mediates between Modbus and SNMP. Then you could view Modbus alarms on your SNMP manager. You could issue commands to your Modbus gear using SNMP SET. That's exactly why Modbus mediation is now available on DPS RTUs, such as the TempDefender G2 and many NetGuardians. With one install, you can get visibility and control of your Modbus controllers, including generators.

Mediate RS-485 or LAN Modbus to SNMP

This is only one example, of course. Modbus controllers are tied to many kinds of equipment beyond generators.

With a Modbus-SNMP converter, you can continue using them.

Plus, when you deploy a TempDefender/NetGuardian RTU as your converter, you'll get to use its user-friendly web interface. You won't have to waste budget dollars on a low quality interface from your Modbus manufacturer.

You'll also avoid using complicated IP-serial converters. Those create wiring hassles and force you to maintain drivers on your servers.

Let's continue with the generator example. With a Modbus-SNMP mediator, you could track important Modbus registers like:

  • Water temperature HIGH.
  • Oil pressure LOW.
  • Engine speed OVER.
  • Engine hours.
  • Battery voltage / alternator output.
  • Generator voltage AC.
  • Generator amps.
  • Fuel level LOW.
Remember that, aside from translating Modbus to SNMP, an RTU is still an RTU. You'll get some discrete points, analog inputs, and control relays to monitor and control other things at your site.

Related Products:

T/Mon NOC | Modbus Bridge.


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