Temperature Switches

Temperature switch
(United Electric Controls)

A temperature switch detects the temperature of some substance. Temperature switches often use bimetallic strips as the temperature-sensing element, the motion of which actuates one or more switch contacts. An alternative design uses a metal bulb filled with a fluid that expands with temperature, causing the switch mechanism to actuate based on the pressure this fluid exerts against a diaphragm or bellows. This latter temperature switch design is really a pressure switch, whose pressure is a direct function of process temperature by virtue of the physics of the entrapped fluid inside the sensing bulb.

The “normal” status of a switch is the resting condition of no stimulation. A temperature switch will be in its “normal” status when it senses minimum temperature (i.e. cold, in some cases a condition colder than ambient). For a temperature switch, “normal” status is any sensed temperature below the trip threshold of the switch.

Like all other process switches, temperature switches exhibit a certain amount of deadband in their switching action. A temperature switch that trips at 300 F rising, for example, will not reset at 300 F falling. That switch would more likely reset at some lower temperature such as 295 F. With mechanical switch designs, some amount of deadband is inevitable due to friction inside the mechanism. However, process switch deadband is actually a useful characteristic as it helps avoid repeated “nuisance” alarms from happening.

To understand this concept, it is helpful to imagine a scenario where the process variable is at or very near the trip point. For our hypothetical temperature switch with a trip point of 300 F (rising), imagine a situation where the process temperature is precisely 300.0 F. Any further rise in temperature will of course trip the switch (sounding an alarm). With no deadband, however, the switch will immediately re-set when the temperature falls back down to 300.0 F. This means the switch may possibly “cycle” back and forth between its trip and reset states with just a minute change in process temperature (300.0 F to 300.1 F and back again). If the temperature switch is activating an alarm every time it trips, it will create a series of alarm events prompting operators to repeatedly acknowledge the alarm. This is a nuisance to operations personnel, as it distracts them from addressing what they already realize is a process problem. It is better for the switch to trip at 300.0 F rising and remain in that tripped state until the temperature falls down to some degree substantially below the trip point. This way, the operators only receive one alarm event rather than multiple alarm events for each process temperature excursion.

Some mechanical temperature switches come equipped with a separate adjustment for deadband (also called differential). Setting this deadband adjustment in a mechanical temperature switch requires the technician to repeatedly subject the sensing element to a rising and falling temperature, to check that the switch trips at the proper setting and resets at the proper setting. This is analogous to cycling the process variable back and forth when adjusting the “zero” and “span” settings of an analog transmitter: checking to see that the transmitter repeatedly outputs a 0% signal at the lower range value (LRV) and a 100% signal at the upper range value (URV). 

For discrete temperature-sensing applications demanding high accuracy and repeatability, electronic temperature switch circuits using thermocouples, RTDs, or thermistors may be used instead of a mechanical (bi-metallic or filled bulb) sensing element. The operation and configuration of discrete electronic temperature switches is very similar to that of continuous electronic temperature transmitters.

An example of an electronic temperature switch module is the United Electric One Series shown below:

UE Series One Electronic Temperature Switch

With electronic temperature switches, the adjustment of deadband (differential) is both precise and flexible. Unlike mechanical switches where deadband is primarily a function of friction, and therefore liable to change over time as the device wears, electronic switching circuits may be precisely set for any trip and reset points along its measurement range, remaining very stable over time.

For more information about temperature switches, contact Miller Energy by visiting https://millerenergy.com or by calling 908-755-6700.

Text adapted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

How Do Pilot Operated Tank Relief Valves Work?

Storage tanks become pressurized when liquid is pumped in and compresses the existing tank vapor. Tanks also become pressurized due to increasing ambient temperatures, which cause the tank vapor to expand. To mitigate damage from these expanding tank vapors, pressure relief valves are installed on tanks to prevent structural damage resulting from over-pressure.

Here is an excellent animation, courtesy of Cashco, that shows how a pilot operated relief vent protects a storage tank from over pressurizing during a pump-in situation or during thermal heating conditions.

For more information on tank relief valves, contact Miller Energy at www.millerenergy.com or by calling 908-755-6700.

Common Instrumentation Requirements for Industrial Boilers

Typical boiler instrumentation layout.
(courtesy of Yokogawa)

Boilers are used in a broad range of industries such as electric power, pharmaceuticals, chemicals, ceramics, and paper and pulp. Amid the rising energy costs, tightening environmental regulations, and increasing awareness of safety as of late, the needs for high efficiency operation, low emission operation, and safe and stable operation of boilers are growing.

In order to ensure the air and fuel are combusted at an optimal ratio, the waste of fuel is eliminated, and the exhaust gas is cleaned, real-time monitoring of the oxygen concentration of combustion gases is required. Equipped with an oxygen sensor unit with a longer life span, the Zirconia Oxygen Analyzer ZR series are capable of measuring an oxygen concentration with high reliability. The Stack Gas Analyzer monitors exhaust gas components such as NOX, SO2, and CO2 in order to ensure low emission operation.

A single-loop controller can be used to properly distribute control functionality. Offering the advantages of flexibility of building distributed control systems, simple maintenance, compatibility with conventional systems, and the like, the YS1000 Series of Single-loop Controllers are ideal for safe and stable operation at low costs.

In order to ensure highly efficient and safely operated boilers, it is also indispensable to accurately monitor the drum level and steam flow rate. The EJA and EJX Series of Differential Pressure Transmitters are capable of measuring the drum level with high stability even in actual applications at high temperatures and high pressures. The DY Series MV TYPE of Vortex Flowmeters with a simple construction employ a built-in sensor to measure the steam mass flow with high reliability.

Yokogawa offers a wide variety of sensors and controllers that are used to monitor and operate boilers, and contributes to increasing the efficiency and environmental performance of boilers, as well as ensuring their safe and stable operation.

Recommended Products for Boiler Applications

• Drum Level Measurement - EJA/EJX transmitters
• Combustion Control - The YS1000 Dual CPU Loop Controller
• Steam Flow Measurement - Digital YEWFLO MV Type
• Combustion Monitoring - Zirconia Oxygen Analyzers and AV550G Multi Oxygen Sensor Converter

For more information in Eastern Pennsylvania, New Jersey, Metro New York or Delaware contact:
Miller Energy by visiting https://millerenergy.com or by calling 908-755-6700 in New Jersey, or 610-363-6200 in Pennsylvania.

Detailed Look at the Yokogawa YS100 Series as a Replacement for the Obsolete Siemens 353

This video is a thorough presentation detailing why and how the Yokogawa YS1000 Series is the best replacement for the obsolete Siemens/Moore 353 controller. It is composed of a series of presentation slides - hit the pause button to focus on any single slide.

https://millerenergy.com 

New Jersey: 908-755-6700 

Pennsylvania: 610-363-6200

Breakthrough Solenoid Valve Technology for Upstream Oil and Gas Heating Equipment

A white paper courtesy of ASCO Division of Emerson Automation

Fuel shutoff valves (ASCO)

Low-temperature stainless steel fuel shutoff valves are usually utilized for on/off control of fuel gas within gas fuel trains in process heating system burners. These systems are widely used by oil and gas firms as well by as original equipment manufacturers (OEMs) that produce gas heating equipment or burner management systems (BMSs) and controls in upstream oil and gas pipelines and tanks.

For valve manufacturers, these uses present a relatively specialized, rather challenging application. Environmental conditions at the point of use are often difficult. Ideally, valves should deliver reliable operation despite constraints on factors ranging from power consumption to service availability. Conversely, outdated controls can pose problems — including poor performance, noncompliance with current regulations, and triggering of environmental concerns.

In recent years, a new generation of solenoid valve technology has been changing the shutoff valve game. Their modern designs provide pipeline and tank heating systems with robust, durable performance; safety; and regulatory compliance — all while increasing efficiency and productivity.

Download the PDF version of "Breakthrough Solenoid Valve Technology for Upstream Oil and Gas Heating Equipment" here, or review it in the embedded document below.

Miller Energy, Inc.
https://millerenergy.com
New Jersey: 908-755-6700
Pennsylvania: 610-363-6200

Breakthrough Solenoid Valve Technology for Upstream Oil and Gas Heating Equipment from Miller Energy, Inc.

Your Best Alternative to Replacing the Obsolete Siemens 353

Yokogawa YS1700 as Replacement for Obsolete Siemens / Moore 353 from Miller Energy, Inc.

An Excellent Replacement for the Discontinued Siemens 353 SLC

The Yokogawa YS1700 is a great replacement to the
discontinued Siemens 353 SLC controller.

The discontinuation of the Siemens 353 SLC controller is a concern to many users of this popular controller. With few alternatives, customers are joking that they'll have to turn to eBay for spare parts. There's a much better solution though. The Yokogawa YS1700 PID loop controller, a drop-in replacement for the Siemens 353 SLC.

The Yokogawa YS1000 Series is the ideal choice for many control applications offering extreme reliability and sophisticated control. This product family has bright, easy-to-read displays, multiple I/O points, and powerful loop tuning. For critical applications, the YS1700 employs dual CPUs for maximum reliability and hard-manual control for added protection. The YS1700’s powerful function block programming allows for custom strategies to control many demanding processes such as boilers and steam generators, PH control, dosing control, and many other demanding plant processes.

To learn more about replacing the Siemens 353 with a Yokogawa YS1700, visit this page or go directly to this link https://millerenergy.com/Siemens-353-Replacement.