Best Practices for Routing Control Signal to Multiple Devices

Isolating transmitters are part of best practice for
retransmitting process signals
Image courtesy of Acromag

Acromag is a globally recognized leader in the design and manufacture of signal conditioning equipment for process measurement and control. On a daily basis they get calls on understanding 4-20 mA current loops and how to wire them with or without power supplies. The application note provided below can serve as a template for wiring Acromag modules, or those of similar design from other manufacturers, in applications. Download and save it for use as a reference when connecting field devices to a PLC, DCS, HMI, etc.

Share your process measurement and control challenges with application specialists, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Isolated Transmitter Wiring Examples from Instrument Specialties, Inc.

Signal Splitter Solves Multiple Device Connection Challenge

Selecting the right I/O modules can solve signal
transmission challenges.
Image courtesy Acromag

Industrial process measurement and control requires the transmission of signals from point to point with no significant distortion. Even with the growing prevalence of wireless signal transmission, over-wire transmission of signals is still a primary means of connecting one device to another.

In the cabled process measurement and control world, the 4 to 20 milliampere signal is generally considered the standard for transmitting analog control and measurement signals over any distance.There is an immense array of instrumentation and controllers available for use with 4-20 mA signals, so expertise in routing and delivering those signals should be part of your process measurement and control skill set.

Like just about everything else, routing 4-20 mA signals presents its own set of challenges that require some thought and planning to overcome. Electrical interference is always a concern and must be prevented from impacting the operation of measurement and control devices. Additionally, there must be sufficient power in the signal loop to accommodate the resistance load of connected devices. There are other considerations, but I'm going to focus on these two.

One scenario that can present significant issues is multiple devices requiring connection to the same signal, but with great distance between them. A simple solution can be implemented using an isolated signal splitter.

Features of these units making them an attractive, single box, solution:

• One 4-20 ma input channel for the measuring or controlling device.
• The input signal is retransmitted as identical isolated 4-20 ma signals
• Galvanic isolation from input to output
• Isolation between channels for safety and increased noise immunity. Fault in one output channel does not impact the operation of the other channels.
• Reliable operation in industrial environments, with protection from RFI, EMI, ESD, and surges.
• Low radiated emissions in accordance with CE requirements. 
• DIN-rail mounting of the unit
• Plug-in terminal blocks

If you have a very long signal loop, connecting multiple devices, consider breaking the devices into two groups that may allow for a substantially shorter cable length for each group. Connect each group to one of the isolated outputs of the splitter, giving each group of instruments the identical signal without the risks or impractically of an excessively long cable run.

There are other devices available that may combine special characteristics that solve your signal transmission and processing challenges. Contact a product specialist and discuss your existing or anticipated project requirements. Combine your process knowledge and experience with the extensive product knowledge of a professional sales engineer and produce the best possible outcome.

Loop Powered Isolated Signal Transmitters and Splitters from Instrument Specialties, Inc.

New Signal Conditioning Modules Offer Bluetooth® Configuration and High Density Installation

High density I/O signal conditioner module
Courtesy Acromag

Acromag, a globally recognized manufacturer of signal conditioning modules and related equipment, announced a new product release earlier this month. The microBlox™ line of signal conditioners provides a wide array of useful features, broad range of I/O signal compatibility, and a very compact high density footprint.

Here is an excerpt from the Acromag newsletter from June 6, 2016.

A full line of microBlox™ isolated signal conditioning modules are now available from Acromag. Offering over 175 models, microBlox uB modules can safely interface a wide variety of voltage, current, temperature, frequency, and other field signals with a ±5V or 0-5V DC output to host measurement & control systems. Users can select modules with fixed ranges or wireless configuration via Bluetooth® wireless technology on an Android™ or iOS® mobile device. Acromag’s free AgilityTM app for smartphones and tablets simplifies setting custom I/O ranges and optional alarm functions. The app can also display input signal values and create sharable trend charts. uB modules snap securely into compact backpanels (no screws) in any mix with 4, 8 or 16-channel capacities. With 1500Vac peak (350Vdc continuous) channel-to-channel and field-to-host isolation, the hot-swappable modules are ideal to front-end data acquisition systems or Acromag remote I/O for communication to Ethernet, Modbus, or Profibus networks. High performance is assured with up to 0.05% accuracy and 130dB noise rejection. Prices start at just $90 per module. 

“Advanced microcontroller and wireless technologies enable microBlox modules to bring greater flexibility and signal processing capabilities into such a small, economical package.” stated Robert Greenfield, Acromag’s marketing & sales director.
The microBlox module’s small size (1.11" x 1.65" x 0.4") and channel-by-channel scalability is ideal for embedded or portable applications such as test stands, defense systems, and process control applications. Well-suited for use in harsh industrial environments, the over-molded modules resist shock, dirt, and moisture with dependable operation from -40 to 85°C. Hazardous location UL/cUL Class 1 Div 2 and ATEX Zone 2 approvals are also available.
Accessories include a selection of backpanels with slots to insert 4, 8, or 16 modules. Fuse clips hold the modules securely without screws for easy insertion/removal. The backpanels support surface or DIN rail mounting and include CJC for use with temperature input modules. Blue LEDs indicate modules that are ready for Bluetooth wireless technology communication. Connections are provided for a 5V power source or a 10-32Vdc supply when used with the plug-in 5V power module. A DB25 header facilitates a single cable connection to interface all uB I/O signals directly to the host data acquisition system.

A consolidated catalog describing the new microBlox™ signal conditioners is included below. Share your signal conditioning and I/O challenges with a a product specialist. Combining your process knowledge with their product application expertise will produce the best solutions.

High Density I/O Modules for Industrial Process Control from Instrument Specialties, Inc.

Guide to Industrial Electrical Grounding

Electrical Grounding

Acromag, a manufacturer of industrial I/O solutions, recently produced a 3-part series on the best practices of grounding electrical equipment. For your convenience, this post combines all three parts of the white paper here into a single document below.

When wiring or connecting circuits, electrical equipment, and electrical instruments, there is a connection that you probably don’t give much thought to, and one that consequently reigns as one of the greatest sources of instrument error and malfunction. That connection is Ground.

Electrical systems must be grounded in order to work properly. The earth often serves as an ideal ground because of its large mass and ability to absorb charge, but ground can be any electrical connection that is able to freely conduct electricity, and grounding a circuit does not always refer to making a physical connection to earth ground.

To learn much more, please read the following document.

The Complete Acromag Guide to Industrial Electrical Grounding from Instrument Specialties, Inc.

The Ins and Outs of Isolation: A Guide to Selecting The Right Instrument Isolator

Isolators (courtesy of Acromag)

The primary function of the isolator is to eliminate ground loops that may exist between two or more instruments. A classic application isolates the control room equipment (computers, PLC, DCS etc.) from field devices which may have different ground potentials. In addition to break ing up ground loops, the isolators protect control room equipment from damaging transient spikes and noise generated in the field. Choosing the proper and most cost-effective isolator requires an understanding of the application and consideration of future expansion requirements.

Isolators are available in 2, 3, and 4 wire configurations. Isolators are further classified as input, output, or 3-way (input, output, power) isolators. Input isolation implies the input signal has no electrical connection to the output and power signals. Output isolation implies the output signal has no connection to the input and power. And similarly, 3-way isolation refers to a situation where there is no electrical path between the input, output, or power.

The technical paper below describes four types of isolators and typical PLC/DCS applications in which they are best suited. Each isolator produces a 4-20mA DC output signal corresponding to the 4-20mA DC input signal.

The Ins and Outs of Isolation: A Guide to Selecting The Right Isolator from Instrument Specialties, Inc.