Thursday, March 29, 2018

Current Transmitters and Switches Simplify Electrical Equipment Monitoring

split core current transmitter current switch
A split core current transmitter can be easily fitted to
existing installations without disconnecting power conductors.
Image courtesy Absolute Process Instruments, Inc.
Electrical machinery and devices are everywhere throughout commercial and industrial settings. Motors are found on a countless variety of machines, including compressors, pumps and conveyors. Electric heating is employed in many production processes, as well as being used as freeze protection for piping systems located in the cold. Gathering information on the operational health of electrical equipment can often be accomplished continuously and in real time, simply by monitoring the electrical current flowing to the utilization equipment.

Two common examples of how electric current monitoring can provide information helpful to operators come to mind.

  • Motors driving pumps, fans, air compressors and refrigeration units often have very predictable load ranges that are reflected in the operating range of the motor current. Deriving a process signal the corresponds to motor current enables the operator or automation system to confirm that the motor is operating on command and within its expected load range. Operation outside of the expected range can be cause for concern and prompt an appropriate response. 
  • Electric heaters for process control, freeze protection, HVAC and other applications will present very predictable levels of operating current. Again, a current measurement can confirm that the heater, or multiple heaters, are operating on command.
The questions of whether electrical equipment operates when a run command is initiated and whether it is operating properly (within its expected range) are basic and essential bits of information for any process or equipment operator. For many types of electrical equipment, a process signal corresponding to electrical current provides useful answers to both questions.

Deriving the process signal for electrical current and delivering it to a local or remote control or automation system is a simple task. Whether installing new equipment wiring, or retrofitting to existing cables, there are standard products for a broad range of applications. Some basic features deliver everything needed.
  • Loop powered device for two wire operation
  • Field selectable sensing range
  • 4-20 mA output
  • Fixed or split core variants to accommodate new or retrofit installations
Implementation is very straight forward. Mount the transmitter in a location where the power conductor can be routed through the sensing core of the unit. These transmitters function in a similar fashion to a clamp-on ammeter. The conductor being measured must pass through the sensing unit. Select the appropriate range for the application with jumpers or switches on the unit. The 4-20 mA output signal will correspond to the selected measurement range. Connect the signal cable to create the 4-20 mA loop and you are ready to go.

Solid core units require the power conductor to be passed through the sensing portion of the unit, so the conductor must be disconnected from the circuit at one end and routed through the unit. If this is not practical, a split core unit can be used. The split core is hinged, and opens like a clamp-on ammeter, allowing installation of the transmitter at any point along the conductor without the need to disconnect.

Share your electrical equipment monitoring requirements and challenges with process measurement specialists. Leverage your own knowledge and experience with their product application expertise to develop effective solutions.

Friday, March 23, 2018

High Pressure In-Line Filters for Instrument and Equipment Protection

in-line process filters and filtration elements
An assortment of in-line process fluid filters.
Image courtesy 3B Filters, Inc.
Industrial, commercial, and scientific processes and operations very often have liquids or gases flowing through them. We use fluids for a wide variety of functions, as a motive force, as a solvent, and countless other things. Anytime a fluid is in use, the design of the devices comprising that system generally rely on a limitation of particulate matter larger than a maximum diameter. Filters are designed to capture and retain foreign matter that might otherwise cause wear, damage, or other unwanted impact in a fluid system.

Filtration assembly selection relies on several factors. Correctly specifying a filtration unit will reduce the potential for adverse impact on the process and achieve the desired level of protection.
  • Media Compatibility - Construction materials for housings or bodies, filter elements, gaskets, and other parts exposed to the process media must accommodate their potential corrosive effects. The inverse is true, as well. The filter unit materials must be evaluated for their potential impact on the media.
  • Temperature - Filter element, housing and gasket components should be compatible with anticipated extremes of process temperature. Some additional headroom never hurts.
  • Pressure - The containing portion of the assembly must be rated to withstand the full range of possible operating pressures, again with a suitable amount of headroom.
  • Flow - Size the filtration unit to handle the full range of process fluid flow without excessive pressure drop.
  • Capture - Survey the needs of instruments or equipment intended to be downstream of the filter. These are the items the filter is protecting. What are the particulate contaminant limits or tolerances of the downstream devices? Whichever has the lowest tolerance for foreign matter is likely the governing element for filter particle size retention. The filter element, whether disposable or cleanable, must be selected to prevent or appropriately limit passage of the  particle size range that will impair operation of the downstream components.
  • Retention - As particulates are trapped by the filter, the unit begins to clog and pressure drop increases. Processes will have varied filter element replacement protocols along the continuum of whether filter elements are changed regularly or left in place until flow impairment. Select a filter element size suitable for the anticipated contaminant load of the process. Higher levels of expected particulates generally indicate a need for a larger filter element to provide the capability to retain the contaminants while still allowing for sufficient passage of clean fluid.
There can be many other considerations for filter selection that may come into play for specific installations. Most important is to not forget to put filtration protection in place. It is cheap insurance against excessive wear and damage to sensitive instrumentation and equipment. Share your filtration requirements and challenges with product application specialists. Leverage your own process knowledge and experience with their product application expertise to develop effective solutions.

Wednesday, March 14, 2018

Bubbler-Tube Liquid Level System

bubbler tube liquid level measurement system
The Type L100 is a complete and ready to use
bubble-tube liquid level measurement system.
Image courtesy ControlAir, Inc.
Measuring liquid level in an open tank or vessel can be accomplished in a number of ways, all of which require some arrangement of instrumentation to either infer the liquid level from the measurement of a related physical property, or directly deliver the liquid level visually using a scaled gauge arrangement. One indirect method of level measurement is often referred to as the bubbler or bubble-tube method, so named because it employs a purging gas that continually vents from the bottom of a tube extending into a tank of liquid. Through a simple apparatus, the level of a liquid can be inferred by the amount a back pressure exerted upon the gas flowing through the tube.

Probably the greatest advantage of this method of liquid level measurement is that the media does not contact the sensing instrumentation, protecting the instrument from damage by the media, and the media from possible contamination from the sensor. The only portion of the apparatus in contact with the liquid is a tube immersed into the tank. Basically, a purge gas flows through the immersion tube and may bubble out the immersed end of the tube, which is open to allow the contained liquid to exert a hydrostatic pressure on the purge gas. The back pressure on the gas that is exerted by the liquid contained within the tank will vary directly with the depth of the liquid. The back pressure can be correlated to a liquid level. Further calculations, which would include the tank shape, dimensions, and the liquid density can provide an indication of the volume and mass of the liquid.

It is feasible to create your own bubbler system, but the cost in human resources to design, coordinate, procure, and assemble all the components is unnecessary. ControlAir provides a completely designed and pre-assembled unit, compact and ready to run on your application. More information is included in the datasheet below. Share your process measurement challenges of all types with measurement specialists. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.
 

Friday, March 9, 2018

Single Loop Process Controllers

process controller with display
One of many single loop process controller variants.
Image courtesy Eurotherm
There are many variants of process controllers, each providing some combination of input, output, interface, alarm and other functional options. They range from simple on/off devices to programmable microprocessor based units providing a wide range of functions in addition to control of a process parameter. 

A single loop controller focuses its function on the regulation of one input value. The control algorithm and output action are directed solely at a single process value. An example would be a temperature controller. A single input from a thermocouple, RTD or other measurement instrument powers the control algorithm, which in turn adjusts the output action to affect any change needed to keep the process valve, or input, at a setpoint. The single input point may be used to drive more than one output, in this example a heating and a cooling output, but a single loop controller is generally limited to one process value input.

Process controllers can deliver an extensive range of auxiliary functions, in addition to straight line process control. The enhanced functionality can negate the need for additional hardware in the form of separate devices and instruments with their added burden of calibration, maintenance and repair. The list of available options is long, but here are some that may prove useful.
  • Alarm outputs that can be programmed to respond to certain input conditions and annunciate a process condition out of the expected range.
  • Retransmisson of the process signal as an analog output for use with other instruments.
  • Flexible configuration via PC to speed setup or change of use.
  • Recipe storage of process control setpoint changes for quick setup for differing batch operations.
  • Customizable alarm messages to enhance operator understanding of their meaning.
  • Communications for integration with larger control systems or data acquisition equipment.
  • Remote setpoint input.
  • Setpoint time or event based profile programming.
  • Universal input section to accommodate wide range of input devices and enable deployment of a common controller model to many applications and locations throughout a facility.
There are more options and functions than can be effectively listed here. Share your process control challenges with a process measurement and control specialist. Effective solutions will arise from leveraging your own process knowledge and experience with their product application expertise.