I have also been published in Facilities Engineering Journal [March/April 2002] with article "What is the True Downtime Cost". (Also referenced by several publisher like MaintenanceResources.com, automation.com
Also Authors Don Fitchett and Mike Sondalini coauthor the extension of the original book -"The True cost of manufacturing downtime - 2nd Edition"
Most of the time when people refer to PLC Troubleshooting, they are actually referring to using the PLC to troubleshoot machine failure more quickly. In this post, we are applying the machine failure analysis to troubleshooting the PLC itself.
Most reading this, already know how the laws of physics are applied to machine failure analysis and used for machinery failure probability assessments. So a company can assess what parts to stock to minimize downtime cost effectively. But we have found many neglect to take into account those basic laws when troubleshooting the PLC itself (and other machine automation equipment). So below is the list again, in order of most likely to least likely just as a reference.
Failure
probability is categorized like this …
(In order of most likely to least likely)
Mechanical
Electro-Mechanical
High Current (because of associated high heat)
Low Current
Solid State
Environment can be
an exception to the general rules.
(Relay card most likely, and
MTBF is useless unless solid state, as frequency PLC program activates,
dictates failure rate as well as environment.)
The
above probability guide translates to PLCs as ...
External to PLC
Output Cards
Input Cards
Power Supply
Backplane
CPU (processor Card)
Environment can change basic
order above. A couple examples, in a foundry, the metal dust causes backplane
to fail more frequently. In the machining industry, penetrating fluid getting
into sensors causes input cards to fail more than output cards because the
liquid causes input card to sink more current than designed to. In wire
manufacturing where a lot of high voltage insulation testing is going on, CPUs
fail more often because control voltage for PLC does not have line filter in
line with it. etc. etc. Other variables that effect the failure rate are
improper design, like not allowing the 20% extra when calculating relay card or
power supply current, etc etc.
To dig deeper into the analysis, lets take a PLC thermal couple input card as an example. You want to decide, should I stock spares of this type of PLC input card? It is an interesting one, as it has no moving parts, but in industrial applications, commonly used in a high heat environment. So its probability of failure could be classified in the more likely categories of mechanical and high current, even though it is not literally mechanical or high current. (The environment in which it commonly operates places it up there with those high probability of failure.)Technically an input card, yet risk at the level of output card due to environment. Point being, while to two priority list above is a general guide, you need to consider your particular environment too. (There are exceptions to every rule. 😊 )
Autonomous Maintenance (AM) is the first step in Total Productive Maintenance (TPM) methodology which is a part of the LEAN manufacturing philosophy.
Autonomous Maintenance Steps:
Step 0 Is the lessor known and practiced autonomous maintenance step, has the goal of educating machine operators on the basic knowledge of machine components functions and maintenance best practices.
Step 1 of autonomous maintenance is cleaning and inspection. Its sole purpose is to remove grime and dirt from the machine in order to identify any problem associated with the machine. In so doing, the operation of the machine is stopped, all fluids drained and all machine covers removed in order to reveal all parts to be cleaned and inspected.
Step 2 sets out to remove causes of contamination in order to improve access. In this stage, the source of the dirt is of the primary concern operators seek how to minimize the sources of contamination.
Step 3 is about the cleaning and lubrication standards. These standards define what the operators should inspect, clean, lubricate and tighten, how it should be done, after what period and such like.
Step 4: The operators should be trained to gain enough expertise on the function of the machine parts and solution finding skills. They are undergo an in depth training to familiarize themselves of the functionality as well as obligations.
Step 5: Conduction of autonomous inspection using the skills and knowledge gained from the first four steps. Tasks are bench-marked with that of other maintenance departments so that scheduling avoids overlapping effort.
Step 6: Implementation of visual maintenance management to make the workplace as visible as possible. Using a Kamishabi board is important as it points out when and what has been completed.
Step 7: The process is based on the principle of continuous improvement. Records of activities done are subjected to auditing regularly. Achievements and failures are iterated to future designs to improve and make maintenance easier.
With AM Step 0 being the key one to insure greater success with all the other steps, you should learn more. Here are some additional resources to help you.
How to measure conductivity of water (conductometry)
Insight to conductivity measurement (conductivity to resistivity)
This How to measure conductivity of water PDF offers insight to conductivity measurement (conductivity to resistivity) using a conductometry meter. Below are excerpts from whitepaper...
Figure No. 1 Traditional two-plate conductivity probe.
Conductivity measurement meter operation and use. The electrical conductivity of water based solutions (and its opposite, conductivity to resistivity) indicate its electrical current carrying ability. High conductivity occurs when many charged atoms and ions are in the water. This typically means the presence of dissolved metals, salts, acidic or alkali chemicals. Conductivity measurement probes are used to measure the total level of charged particles present. This article explains how conductivity measurement probes work and their application in boiler water treatment and management.
The more charged particles that are present, the easier it is for the electricity to flow. The amount of electricity that flows is a direct reflection of the amount of chemicals present in the water. Conductivity measurement, measures the Total Dissolved Solids (TDS) present and can be used as an indication of contamination. Some charged particles contribute more than others. Organic compounds, like fuels, oils, alcohols, sugars, do not behave in the same way and conductivity cannot be used as a measure of contamination.
Conductivity measurement:
To pass electric current through water a conductivity meter has two probes a small distance apart. A known amount of electricity is put down one probe and the amount that gets through to the other probe is measured. The greater the electric current, the greater the number of charged particles present in the water. Figure No. 1 shows how the earliest conductivity probes were designed. To make the probes more sensitive when fewer charged particles were present the distance between the plates was reduced.
The size of the plates/probes and their distance apart establishes a cell constant for the probe. The meter’s sensitivity can be selected by choosing the probe’s cell constant. Low conduction solutions require big probe surface areas close together while highly conducting solutions use smaller surfaces further apart. Click to learn more about how to measure conductivity of water.
Conductometry probes:
The sensor end of the probe is mounted in the water stream and the read-out is displayed locally or in a control room. Conductivity meters are regularly installed in boiler water purification plants to prove the treatment is removing the dissolved salts and metals that would otherwise go into the boiler and scale-up the heat transferring metal surfaces.
Conductivity meters are also used to measure the TDS build-up inside boilers and to automatically open and close a control valve to blow down the boiler contents and lower the TDS. The probe senses the contamination increasing as water is boiled away into steam. Once the conductivity is above a set limit the automated blow down valve opens and discharges the high TDS water. The probe also monitors the falling TDS levels in the boiler and shuts the blow down valve when the lower set point is reached. Click to learn more about how to measure conductivity of water.
References: Process Control Operative Certificate in Chemical Plant Skills, Holmesglen Collage of TAFE.
Aquarius Technical Bulletin #2, Aquarius Technologies P/L
The PLC Professor will make you well prepared to take on PACs & RSLogix 5000!
Starring The PLCProfessor!
Business Industrial Network will be providing their 3 day hands-on RSLogix 5000 PAC training seminar/workshop in St. Louis, MO on September 26-28, 2017. The instructor will be The PLCProfessor (Tim), guiding the class through hands-on exercises using a real PAC (Process Automation Controllers), CompactLogix.
If you have been doing a little research about PLC Training on YouTube, you may have watch Tim (The PLCProfessor) deliver PLC training. Now is your chance to learn about PACs from him, first hand, in person, with hands on real equipment!
BIN95, with over a 2 decade reputation for delivering "The Best for Less", did not cut any corners here either. Every attendee will also receive the following at no additional cost!
A free copy of the RSLogix 5000 programming lab project manual ($150 value)
Variable Frequency
Drive Essential, is a VFD training online certificate course where you learn how VFD motor control works and other essentials. The online course is designed to familiarize students from beginner or expert with the essential VFD types, features, functions and benefits of them. Be it a VFD pump, motor inverter or other AC motor speed control.
VFD Basics Video
Transcript:
Welcome to Business Industrial Network (BIN95.com)
This training this module will cover variable frequency drive essentials. It is designed to provide product knowledge for all levels. At the conclusion of this module you can register to receive your certificate of completion. Be sure to take advantage of obtaining this documentation serve as proof that you completed the online course.
Now let's get started! PID control is a very popular application for industrial processes the letters stand for Proportional Integral and Derivative. The three calculations that comprise that is sometimes called a Loop. It incorporates an algorithm or formula. It makes calculations of the process and provides feedback to the controller that allows the desired output. An entire session could be developed to cover this topic in detail. A simple explanation however might be to examine a cruise control system on an automobile. A driver sets a desired speed and the controller takes into account varying conditions such as wind conditions and inclines. As the controller senses the varying conditions calculations are being made to ensure the desired speed is maintained.
Here is the block diagram representing the process. Note that each element has its own formula. It looks complicated but the operator merely needs input a few values and the controller then takes over the process. We'll examine this concept in more detail later in this module. No doubt the single biggest market for VFDs are into the HVAC industry. You will hear this acronym a lot when discussing drives. It stands for heating ventilation and air conditioning. Many reports site that 15% of the world's energy consumption is from motors used in HVAC application! That's right ceilings of every commercial and industrial building are a multitude of motors that provide heating and ventilation for areas inside the building. These are fans, air-conditioning units and exhaust systems. During low occupancy can adjust the speed motors are running thereby saving money on electric consumption by as much as 3 see how this is accomplished a little later on in our discussion.
Variable frequency drives are set up by using the keypad on the drive. This key pad is also used to run drive. Some drives automatically going to the run mode. It can be easily changed to the monitor mode by toggling the membrane mode switch again pressing the mode switch. It is important to note in programming manufacturers. In this instance, the Schneider Altivar 212 uses the "symbol ""tHr"" for inputting the thermal" overload value. Most drives can be set up very easily for routine applications by inputting information from the motor nameplate. Namely motor current nominal voltage and desired overload current level the same as the full load current of motor. Many manufacturers offer an alternative LCD keypad with English text that spells out the function rather than provide a symbol. In those cases, interchanged with a standard supplied keypad or as a remote mounted kit. Coming up we'll talk about the other VFD functions available from most drive manufacturers.
In the definition VFDs varied the speed of an AC motor. Well then at full speed the desired speed? This practice would be equivalent to driving a car with the accelerator pressed to the floor applying a brake with your left foot to meet the desired speed limit. And that sounds a little bit far-fetched. But variable frequency drive allows for energy efficiency by only utilizing the exact amount of power operate at a speed that load requires. In addition, the amount of mechanical stress the equipment are minimized. Lastly some applications as we will see such as conveyors smooth operation and changes in speeds offered by a VFD. A typical sewage treatment plant utilizing these equipment applications. This equipment will run an optimized electric power while eliminating mechanical stress and saving money on cost and maintenance. A popular application for pumps and compressors is a duplex design. In pump applications and alternator is used with either a pressure transducer or a float switch. In these applications starts when the pressure is required. As the initial pump comes up to full speed more pressure is required pump starts. Once the system is satisfied ...
Drive manufacturers have the ability to accept feedback signals PID loop refers to the cycle of control. Open loop feedback going directly to the drive. A closed loop system however accurate control of the drive. In closed-loop applications and a speed reference are programed. If the actual
speed varies from the setpoint, referred to as an "off the set point", offset for short. Let's recap that happened ...
The marketplace is jam-packed with manufacturers variable frequency drives. This slide will feature some of them. Eaton electrical has wide variety of drives from different applications. One popular segment of the line is their SVX 9 general purpose and SPX 9 high-performance models. Much of this offering are Bakken drives re-branded for Eaton. Franklin electric out of Portland Oregon's their p- series type for high performance. And PowerFlex 755 for the harmonic mitigating drives. Siemens labels their drives Micro Master SiMatic and SiMotion. They cover a wide variety of applications including HVAC. Some manufacturers will offer low end VFDs as part of their line. These are labeled as micro and mini. they are also sold in board level designs. Micro is the smallest features. Mini offering a few more features such as a display readout. Popular among OEM's are board level versions of these drives. OEM's mounted in their equipment...
Let's take some time to go over the standards that apply the variable frequency drives. NEMA Electrical Manufacturers Association a standard title NEMA ICS 618 This applies the general purpose adjustable frequency drives that include power conversion AC motor or motors. This also applies to systems connected to live voltages of the 1 kV AC 5 frequency up to 6 Commission has issued electromagnetic capability adjustable speed electrical power drive systems part 3 requirements and specific test methods. The CE mark has become ...
Now why do engineer is specified bypass on drives? he primary reason is to keep machines critical nature from the 197 early stages of development. There are many failures with the circuit boards and SCRs. Customers were anxious to obtain energy savings but the high failure rates caused manufacturers to offer bypass packages as a backup. Bypass was considered low-cost method to keep the motor running in case of a VFD going down. Today's VFD failure rates are much lower than bypass contactors. Therefore, the costs appropriated for bypass components in some cases channeling toward a spare drive. This is especially important is a backup for several drives inside a plant. Redundant VFDs critical applications. As seen here they work on the principle that if one VFD fails maintained by a second VFD automatically takes over. Redundant VFDs have been around for years only recently has this concept become cost effective. As the VFD...
Variable frequency drives their compact size into existing motor control centers. Replacing the standard starter or multi speed starter This represents a considerable energy savings opportunity for customers. However, caution needs to be exercised since the VFDs generate considerable more heat than a conventional motor starter. Proper ventilation needs to be addressed. Also...
Let's go through the selection factors that apply the variable frequency drives. You need to know the horsepower voltage and if the voltage is single-phase or three- phase. Next you need to know whether it's constant torque or variable torque. Next you will need to now of a disconnect is required disconnect is required breaker for a switch and the current rating or fuse clip rating that applies. Next you need to find out if an output contactor is required. If an input line reactor is required or a load reactor. If dynamic braking is required. And then bypass is required or three contactors required. What are the pilot lights and switches required the bypass operation? Is redundancy required to now the NEMA or IP rating of the enclosure. And lastly if any special boards are needed interfacing with network system or with an encoder.
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