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Protecting Against Noise in Thermocouple Installations

Thermocouples are widely used to measure temperature because they are durable, affordable, and have a wide temperature range. A thermocouple is formed by the joining of two different metal alloys at a common point referred to as the measuring or hot junction. Thermocouple lead wires attach to a temperature measuring instrument at a second connection point called the reference or cold junction. When the hot junction is heated, the thermocouple generate a very modest DC voltage. The tiny voltage signal is detected by the temperature measuring instrument and converted to a temperature reading. 

Thermocouples produce voltages in the millivolt range, with microvolt changes per degree C temperature change.  The signal (voltage) of a standard thermocouple is low, on the order of 10 mV, and the signal-to-noise ratio can rapidly drop in the presence of the types of electrical noise seen in most industrial situations. A small amount of noise can have a significant impact on precise measurement. 

There are numerous sources of noise that can interfere with thermocouple measurements.  The three most typical sources of noise are as follows: 

Common Mode Noise from Ground Loops  

Common mode noise generates an undesirable voltage on both leads of the thermocouple. Common mode noise is typically induced by a ground loop, which occurs when a system has a potential difference between two grounds. Because the tip of a thermocouple is a bare wire junction, a ground loop might form. If the tip is grounded where it is detecting temperature and that ground is at a different potential than the ground at the thermocouple's measuring end, a ground loop forms and current flows. 

Normal Mode Noise from Electromagnetic Fields  

Normal mode noise generates a current that flows in the opposite direction as the measuring current. This form of noise is often created by massive alternating current current sources, such as power lines, which generate a magnetic field. The magnetic field, in turn, generates a current in the measurement path. Motors, lights, and power lines are examples of high-current devices. Normal mode noise is typically at 50/60 Hz line frequency. The normal mode error current is proportional to the field intensity, the size of the loop, and the loop's orientation to the field. 

Electrostatic Noise from Rotating Equipment

Stray capacitance introduces electrostatic noise into the measuring path. Electrostatic noise is created by rotating equipment, which generates an alternating current (AC) current that is capacitively connected into the measurement route. Electrostatic noise can be coupled by stray capacitance through the tip of a thermocouple. 

The following procedures will significantly reduce thermocouple susceptibility to electrical noise in an industrial setting. 

• Twist and foil shield the extension or lead wires from the thermocouple to the measurement instrument. Twisting wires together minimizes both outgoing and incoming noise caused by electromagnetic interference. Each wire in the circuit carries voltages that are both equal and diametrically opposed. The voltages on the two lines are the same, but the polarity is reversed. The polarity of the magnetic field formed around the wire is determined by the polarity of the electric voltage going through the wire. Not only is the polarity of the electric voltage on each wire opposite, but so is the polarity of the magnetic fields radiating from each wire. When equal but opposing forces collide, they cancel each other out. 
• Ground the measurement junction at the point of measurement. The grounding is typically to the inside of the stainless steel sheath that covers the actual thermocouple. The advantage of grounding the measurement junction is that the electrical noise is distributed equally on each wire of the thermocouple.
• Use a transmitter with excellent common mode voltage rejection and position it as close to the thermocouple as possible.

Duro-Sense Corporation
310-533-6877
https://duro-sense.com

Critical Electricity Generation on Offshore Oil Platforms Rely on Robust Engine-Compressor Thermocouple Design

Powering a wide range of complex equipment on offshore oil and gas installations necessitates a considerable amount of continuous electricity. Pumps, valve operators, critical communications, turntables, engines, and safety devices are just a few examples of the drilling and processing environment that require a dependable power source. A vast amount of electrical power, comparable to that of a small town, is needed. Heaters, air conditioners, water desalination, food storage, and even trash processing need electricity from electric generators. 

The circumstances on offshore sites are challenging. Equipment and components must be sturdy to perform correctly and reduce the need for routine maintenance.

Temperature is one of the most crucial measuring factors for a compressor, and its precision directly impacts compressor efficiency. According to the findings, temperature calculation errors account for more than 80% of efficiency errors. More aspects of compressor temperature measurement, as well as improved temperature measurement methods, are required. Thermocouples measure the temperature of the inter-stage gas compressor and the temperature of the exit gas. 

In these applications, a specialized temperature sensor called an 'engine-compressor thermocouple' detects temperature. These are heavy-duty temperature sensors that detect several factors, such as exhaust gases and lubricant temperatures. Such sensors have been time-tested and built to survive offshore maritime environments' extreme mechanical and climatic conditions. The thermocouple must be robust enough to endure high vibration and corrosive environments while being accurate and fast responding. 

The engine-compressor thermocouple offers oil and gas platform personnel precise measurements, high precision, and quick response times. Additionally, engine-compressor thermocouples are easily calibrated, removed, and replaced if necessary.

Duro-Sense Corporation
310-533-6877
https://duro-sense.com

Please take a moment this Memorial Day to honor those that served our nation and are no longer with us.

The "Big Eight" Thermocouple Types

In the United States, each thermocouple class carries a notation defined by a single letter. The Instrument Society of America (ISA) pioneered this method, which was introduced as an American Standard in 1964 to avoid proprietary names. The American National Standards Institute (ANSI-MC96.1, 1982) and the American Society for Testing and Materials (ASTM 230-87) use the National Institute of Standards and Technology Monograph 125 reference tables as the basis for standardization. As noted in the ANSI and ASTM standards, the letter designations define the tables. Thus, they may be applied to any thermocouple with a temperature-EMF relationship that agrees within the tolerances defined in the standards, irrespective of the thermocouple's composition. 

Only a few of the approximately 300 different temperature measuring thermocouples defined and tested have achieved mass acceptance because they exhibit more desirable electrical and physical characteristics. Resultantly, these eight preferred thermocouple types are the most widely used in industrial, commercial, medical, and aerospace applications. 

1. Type B = platinum- 30% rhodium/platinum-6% rhodium - 0 to 1820°C *
2. Type E = nickel-chromium alloy/a copper-nickel alloy -270 to 1000°C*
3. Type J = iron/another slightly different copper-nickel alloy -210 to 1200°C*
4. Type K = nickel - chromium alloy/nickel - aluminum alloy -270 to 1260°C
5. Type N = nickel-chromium-silicon alloy nickel-silicon alloy -270 to 1300°C*
6. Type R = platinum- 13% rhodium/platinum -50 to 1768°C*
7. Type S = platinum- 10% rhodium/platinum -50 to 1768°C*
8. Type T = copper/a copper-nickel alloy -270 to 400°C*

* temperature range as per NIST Table I: Thermocouple Types Definitions.

Certain combinations of alloys, such as Type J and K, have become popular as industry standards.  Cost, availability, melting point, chemical properties, stability, and output are all drivers for thermocouple application. Different types of thermocouples are best suited for different uses/applications. Thermocouple selection also depends on the temperature range and accuracy needed. Other selection criteria include the chemical inertness of the thermocouple material and whether it is magnetic or not. 

For more information about thermocouples, contact Duro-Sense by calling 310-533-6877 or visiting https://duro-sense.com.

Shorter Lead Times Make Happier Customers

Customer satisfaction and loyalty can be closely tied to how quickly customers receive their orders. In terms of supply chain, lead time is a big part of any successful business. Reducing lead times as much as possible is vital to a company’s success.

Manufacturing lead time is the total time required to manufacture an item. From an operational standpoint, One should be aware that there are many different types of lead times:

• Material lead time is the amount of time it takes a customer to place an order with a supplier and receive it; from when the order was confirmed to when they have it on hand.
• Pre-production lead time is the amount of time required for the supplier to create a work order. This is sometimes called planning time. It primarily takes the form of paperwork.
• Production or Factory lead time is the actual amount of time the supplier needs to manufacture the product.
• Post-production lead time is the time required for a customer to receive an item from dock to inventory. Depending on the product, it could entail anything from inspection to quarantine time.
• Fixed lead time refers to a part of production or factory lead time that is not dependent on the order quantity.
• Variable lead time, is the part of production or factory lead time that is dependent on the order quantity.
• Cumulative lead time is the term used to describe the entire amount of time required, from order confirmation to the delivery of the product. It is the aggregate of material lead time and production or factory lead time

Accurately forecasting and reducing lead time is a vital element of any manufacturing operation. The need for a timely and accurate response to inquiries, on-time order completion, and the ability to respond quickly in an emergency must be at the core of a manufacturer’s ideals. They are keys to maintaining customer satisfaction, a competitive advantage, and a definitive reputation in the marketplace.

Duro-Sense has spent years researching, analyzing and implementing methods and procedures to continually improve our ability to work efficiently in pre-production and production, and to enable us to respond quickly and seamlessly to a customer’s requirements and unexpected emergencies.

Strategies including:

• Supply chain re-evaluation
• Domestic material sourcing
• Warehouse reorganization
• Creative inventory control
• Re-training and cross-training personnel
• Improved information flow and accuracy

This approach, has given us the ability to have more efficient and streamlined production and customer interaction, which leads to faster response time and shorter lead times. Duro-Sense has moved to the forefront of on-time delivery and the ability to seamlessly adapt to any urgent customer need.

Customers don’t like waiting. Production lead time can be the critical component in the success of your business. Like a bad movie, or a dull and tedious speech, shorter is always better. Choosing the right manufacturer is essential when trying to calculate lead time. After over four decades in manufacturing, Duro-Sense has developed valuable strategies regarding the most effective ways to reduce lead times without compromising quality. Let us prove it to you.

Duro-Sense Corporation
310-533-6877
https://duro-sense.com