6 Things OEM Design Engineers Need to Know

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When considering the purchase of pressure transducer for inclusion in a refrigerator chiller, pump, pump skid, engine test equipment or other machinery to be built and shipped to an end user, one must seriously consider the manufacturing environment. A transducer's successful operation and life are directly related to the system design and assembly processes.

Original Equipment Manufacturers (OEMs) that follow a strict Design for Manufacturing and Assembly (DFMA) methodology will have few, if any, transducer problems. In addition, they will enjoy fewer part numbers, lower costs, and longer machine life. OEMs that do not adhere to DFMA practices increase the probability to encounter various issues, including transducer problems and failures.

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6 Things OEM Design Engineers Need to Know

  1. 1. 1 6 THINGS OEM DESIGN ENGINEERS NEED TO KNOW About the Manufacturing Environment Before They Specify a Pressure Transducer When selecting a pressure transducers for use within a refrigeration chiller, pump, pump skid, engine test equipment or other machinery to be built and shipped to an end-user, the manufacturing environment should be considered. A transducer’s successful operation and life are directly related to the system design and assembly processes. Original Equipment Manufacturers (OEMs) that follow a strict Design for Manufacturing and Assembly (DFMA) methodology will have few, if any, transducer problems. Other benefits include fewer part numbers, lower costs and longer machine life. OEMs that do not adhere to DFMA practices increase the likelihood of reoccurring issues, including transducer failure. Today’s transducers are designed to be rugged enough to withstand excessive temperature, voltage, electromagnetic inference/radio-frequency inference (EMI/RFI), shock, handling and overpressure. However, if transducers are subjected to a manufacturing environment that exceeds the supplier’s specified limits of these variables during storage or assembly, sensor issues will occur. It’s easy to forget that a pressure transducer is a highly engineered piece of electrical equipment, due to its small footprint and resemblance to simple mechan- ical components. An OEM design engineer should take note of the following six conditions while designing a system to be manufactured and shipped to a customer. 1. Temperature Excessively high temperatures are a common source of pressure transducer issues. Like most other electronic equipment, they consist of numerous components that only function within specified temperature ranges.Transducers that are exposed to temperatures exceed- ing those ranges during the assembly process can be negatively affected. For example, if an OEM is welding directly next to a transducer, the heat generated from the welder could cause the transducer circuit board solder to reflow. This will result in open cir- cuits or bad joints, causing faulty readings or intermittent problems before or after shipping to the end-user. WHITEPAPER What’s Inside Section 1: Temperature Section 2: Voltage Spikes Section 3: Fluorescent Lighting Section 4: EMI/RFI Section 5: Shock & Vibration Section 6: Overpressure
  2. 2. 2 Similarly, a transducer could be damaged by a heat gun used to shrink wrap a chiller if ex- cessive heat is applied within inches of the sensor. Operators must be aware of the harmful effects this can have on pressure transducers, so preventative actions can be taken. Although the machine is being built on the OEM’s manufacturing floor, consideration should also be given to the environment where the machine will be installed. For instance, a pres- sure transducer installed on a steam line very close to where the steam is being generated will cause a negative change in the dynamics of the sensor. In this case, a simple solution can be to move the transducer further away from the steam line. 2. Voltage Spikes Voltage spikes are another potential problem that can impact transducer function after being installed in machinery on the OEM’s manufacturing floor. Voltage spikes are short durations of electrical transients in voltage. These high-energy surges only last a few milli- seconds, but still can cause damage. They are often extremely difficult to trace unless the source is obvious, such as lightning. Beyond the obvious, OEM engineers should think about potential causes of voltage spikes. For example, an OEM’s customer mounted a pressure transducer on a chiller’s water pipe. The customer was unaware of an arc welding operation in an adjacent building that used a ground clamp on that same water pipe. Intermittent arc restrikes induced large sporadic voltage spikes that were carried through the pipe and water to the transducer, destroying its circuitry. OEM engineers must be aware of their entire manufacturing environment and beyond for potential risks for failure. A conversation with the pressure transducer supplier can be helpful in identifying and eliminating this type of problem. Another potential source of voltage spikes in the manufacturing environment is the electro- static painting process. Painting often occurs after an OEM completely assembles a refrig- eration chiller, for example. In electrostatic painting an electrode is attached to the chiller’s metal surface to ground it. The sprayed paint has a positive charge, which is attracted to the negatively charged metal as if it were a magnet. Although electrostatic painting is an effi- cient, durable and cost-effective industrial method of coating, it must be considered when designing and planning for transducer installation. If voltage spikes have been a reoccurring problem, contact the engineering department about the use of AC voltage stabilizers, zener diodes or other voltage limiting strategies. 3. Fluorescent Lighting Fluorescent lighting can also be a problem for pressure transducers. Fluorescent lamps re- quire an initial high voltage to start the electrical arc through the argon and mercury, which heats the mercury until it becomes a gas.This initial voltage spike presents a potential prob- lem for pressure transducers. Additionally, the magnetic field that fluorescent lighting cre- ates can induce voltages into transducer wires, which the control system may misinterpret as an actual output signal. As a result of these issues, transducers should not be located underneath or within close proximity to fluorescent lighting. 4. EMI/RFI A pressure transducer converts pressure into an electrical signal and is by nature susceptible to the negative effects of electromagnetic emissions or electrical disturbances. Transducer manufacturers do their best to protect the transducer from outside disturbances, but cer- tain design considerations could reduce or prevent EMI/RFI effects.
  3. 3. 3 It is recommended to locate motor generator sets at a safe distance from machinery in- stalled with transducers and its associated wiring to prevent faulty signals and other trou- bles caused by induced voltage. Other EMI/RFI sources to avoid include contractors, power lines, computers, walkie talkies, cell phones and large machinery that produce varying mag- netic fields. The most common ways of reducing EMI/RFI noise are shielding, filtering and suppression. Contact the pressure transducer manufacturer for help on how these preven- tative measures can be implemented. OEMs that follow National Electrical Code (NEC) guidelines, run low voltage lines in con- duits separate from high voltage raceways, such as for a pump skid application. Other OEMs, however, run power and signal cables in the same conduit. As a result, they may experience signal lines with extra induced voltage, which may run the length of the low voltage wires, presenting a possible electrical problem for an application like pump skids. Also, it is advisable for OEMs to have different power sources for the transducer and con- trol system. The risk comes from de-energized relays in the control circuit creating back an electromagnetic field (EMF) that will travel to the power source, causing a voltage spike. If it’s more than the supplier’s maximum rated voltage, the transducer will be permanently damaged and burn marks can be visible on the circuitry. 5. Shock & Vibration Shock and vibration are two potential mechanical problems for transducers. Shock is a sud- den, unexpected impact that transmits energy to a device in a relatively short time interval. For a transducer, that energy passes through the stainless steel up through the housing. Shock may originate from rough transportation and handling, sources includes trucks, fork- lifts and conveyors. Alternately, shock can be caused by dropping the transducer on the shop floor or by an assembler slamming a cabinet door adjacent to it. A transducer may not be damaged by a single shock, but can experience fatigue failure with numerous low level shocks over the course of its life. Vibration can be defined as the continuous oscillation directed at the transducer. For exam- ple, in an engine test cell, the running engine emits a constant vibration that might affect transducer operation if its mounted too close. Shock and vibration can cause a wide range of problems, including dented enclosures, dis- connected wires, broken circuit boards, faulty signals, intermittent problems and shortened life. To prevent shock and vibration during the assembly procedure, OEMs should first real- ize this potential problem and take appropriate measures to prevent it. A simple solution is to install transducers as remotely as possible from obvious sources of shock and vibration. Depending on the installation, another possible solution can be the use of shock and vibra- tion isolators. Transducer suppliers can provide OEMs with information needed to design a system where the transducer can be handled appropriately during installation. They advise engineers to design their transducer installation so only a few tools are used for its assembly, increas- ing the likelihood that the correct tool will be used. For example, assemblers shouldn’t use channel locks that may gouge and scratch the pipe when a standard open-end wrench will work. If the assembly is heavier than the approved weight limit, assure enough people are involved in the lifting he assembly to avoid damage.
  4. 4. 4 6. Overpressure Once an OEM has assembled the machine, either on their manufacturing floor or at the end user’s location, be aware of overpressure. Causes of overpressure include fluid hammer, un- intentional heat applied to the system and a faulty pressure regulator. Pressure transducers can withstand occasional pressures up to their proof pressure rating, eventually returning to their natural state. Pressures that reach burst pressure can rupture the diaphragm or case and cause leakage. Pressures above proof but below burst pressure can result in permanent diaphragm deformation, causing an output shift. To prevent overpressure, OEM engineers must understand the dynamics of their system and the limits of the transducer. As they design it, they need to be aware of the interaction of pumps, control valves, balancing valves, check valves, pressure switches, motors, com- pressors, tanks and other system components. They should consider how the interaction of these devices can lead to problems like overpressure and design a system that will prevent them. In addition, OEMs must be conscious of pressure swings in their own system. A review of service calls, warranty claims and conversations with service personnel will reveal the caus- es and ranges of actual overpressure occurrences. Engineers can then design a better sys- tem and select the proper transducer for it. OEM engineers have the responsibility of designing a machine or system that will work effectively with minimal problems, first in their own manufacturing environment and lat- er at their customer’s facility. OEMs that follow a strict DFMA methodology enjoy the cost benefits. The first step in accomplishing this is to thoroughly understand the system and eliminate problems that have occurred in previous designs. Remember to factor in the de- sign conditions for temperature, voltage, EMI/RFI, shock, handling and overpressure that could be exposed to the equipment. Once those variables are identified, select pressure transducers and other equipment that will work effectively in that environment. A pressure transducer manufacturer can also provide technical assistance or recommendations during the design phase of project. The result will be a highly efficient, trouble-free machine or system that requires limited maintenance and will exceed its rated service lifetime. About Setra: Founded by former professors of Engineering at Massachusetts Institute of Technology (M.I.T.), Setra has been designing and manufacturing sensor products since 1967. Our specialty is in the pressure and sensing in a wide range of markets including HVAC/R building automation, pharmaceutical, energy, medical sterilization, industrial OEM, test & measurement, meteorology and semiconductor. Setra Creates Solutions: Over 40 years of expertise in sensing and sensing applications R&D and Design Engineerings focused providing application solutions Sensors cover a wide range of pressure rages with unique expertise in low pressures Sales and manufacturing in the U.S., Europe, and Asia for fast solutions and products

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