Showing posts with label UEC. Show all posts
Showing posts with label UEC. Show all posts

Programming the UE One Series Hybrid Transmitter-Switches


The United Electric Controls One Series electronic pressure and temperature transmitter-switches are designed to provide transmitter, switch and gauge functions all-in-one rugged enclosure that can withstand the rigors of harsh and hazardous environments. Available in Type 4X enclosures approved for intrinsic safety, flameproof and non-incendive area classifications, these hybrid transmitter-switches have a fully adjustable set point and deadband and 0.1% repeatability. This video provides a quick tutorial on how to set up the One Series.

For more information, contact Miller Energy. Call them at 800-631-5454 or visit their web site at https://millerenergy.com.

Temperature Switches

temperature switch
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.

switch contacts

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
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 to Select a Pressure Switch

UEC One Series Switch Transmitter Hybrid
UEC One Series Switch Transmitter Hybrid
Reprinted with permission from United Electric Controls

Pressure switches are widely used by many industries and within many applications. The basic function of a pressure switch is to detect a pressure change and convert it into an electrical signal function – typically on/off or off/on. Pressure switches may be of electro-mechanical or electronic/solid-state design (see our ONE Series); and while each may have its advantages, arriving at the correct pressure switch for your application is the same.

Set Point & Deadband


Application set point (sp) is the desired value reached at rising or falling pressure at which the micro-switch changes electrical states. Depending upon the pressure switch function, the micro-switch could be wired to open (turn something OFF)  or close (turn something ON) when set point is achieved, thereby triggering an event such as an alarm, equipment shutdown, or powering up secondary equipment. Ideally, the set point should fall into the mid 50% of the pressure switch range for best performance including repeatability and long life. On an electro-mechanical pressure switch, set point may be adjusted internally or externally either through blind adjustment or reference dial. An electronic pressure switch would have internal or external adjustment via a key pad and digital display or a handheld programmer.
Deadband graph

Deadband (DB) is the on-off differential required to reset the micro-switch. This value may be fixed or adjustable with an electro-mechanical switch and may be up to 100% adjustable on an electronic switch.

Deadband may be an important factor to consider depending upon the application requirements.

System Pressure


Knowing your normal and maximum system pressures will help in selecting a pressure switch with appropriate minimum and maximum operating parameters. Once your set point is established, other factors to consider are vacuum and/or surge pressure that could affect switch operation. This would involve maximum working pressure, over range pressure, and proof pressure specifications of a pressure switch. The relationship between set point and system pressure has a direct effect on switch performance and life.

Electrical Considerations


UEC 100 Series Pressure Switch
UEC 100 Series Pressure Switch
Micro-switches are available in a variety of configurations. The most common for electro-mechanical pressure switches is 15A, 480VAC SPDT (single pole, double throw). The advantage of a SPDT micro-switch is that it offers wiring flexibility to either open or close on pressure change. Other micro-switches available include 1A with gold contacts, useful when working with a PLC, or at the upper end, 30A when switching certain high voltage heaters or motors. Adjustable micro-switches help with deadband adjustment. A DPDT (double pole, double throw) micro-switch would provide two simultaneous functions off of one micro-switch. If a low-high limit alarm and shutdown were required, there are pressure switches that include two SPDT micro-switches that are independently settable.

An electronic pressure switch would use solid-state relays to change states. Like an electro-mechanical switch, the electronic switch can be programmed to open or close on rising or falling pressure. There are different capacities for switching voltage and current depending upon the application requirements.

Process Media and Wetted Parts


The pressure connection and sensor are known as wetted parts since they come into direct contact with the process media. Sensor material is either elastomer (i.e. Buna-N, Teflon®) or metallic (i.e. Brass, Stainless Steel) with metallic or composite pressure connections. The process media must be compatible with the wetted parts material. Process media temperature should also be considered as each of the different wetted materials would have differing operating properties.

Pressure Switch Mounting


If the unit is to be installed directly onto the process, there are many methods of installation.
Typically a 1/8”, 1/4”, or 1/2” NPT (national pipe thread taper) connection is used with a mating
fitting to secure the pressure switch to the process. There are also straight threaded (SAE, BSPT)
connections, flush mount connections, and sanitary connections. The pressure switch may be
mounted directly in the process line using the threaded connection, a manifold, or flange; or the
enclosure could be bolted to a mounting plate or other plane to secure it. If heavy vibration is
present, you may choose to use a remote diaphragm seal with the pressure switch. The diaphragm
seal mates with the process connection while the pressure switch enclosure is mounted securely
away from the vibration. 

Process Environment


It is important to know what type of environment the pressure switch would be installed in – hazardous or ordinary location; indoors or outdoors; exposed to salt air; inside a control panel; in high ambient temperature. These are just some of the factors to consider so the right enclosure type is chosen. Enclosure types come in many shapes, sizes, and materials. They also conform to various industry and third-party approval standards. Electronic switches can be used to replace electro-mechanical switches when SIL is needed for safety applications.  There are also electro-mechanical pressure switches without enclosures; typically used in OEM, non-hazardous locations where the environment is benign.

With careful consideration of all the factors listed above, choosing a pressure switch is a snap. If you are at all unsure, please contact your local United Electric Distributor or visit the UE Product Selector to find your pressure switch.

Pressure Switches - The Stalwart of Pressure Instrumentation

pressure switch
Pressure switch in an
explosion-proof housing.
(United Electric)
A pressure switch is an electromechanical device that detects the presence of fluid pressure and responds by opening or closing an electrical or pneumatic circuit.

In heavy industry, pressure switches are used in virtually every power plant, refinery, chemical plant, paper mill, steel mill, or other manufacturing plant that blends ingredients.

Pressure switches are simple devices. They can be broken down to their major parts: a pressure port or connection; a sensor that moves in relationship to changing pressures; an electrical or pneumatic switch that opens or closes upon movement; and finally a housing that protect the internals of the pressure switch from the ambient conditions.

pressure switch
Differential pressure switch.
(United Electric)
Pressure switches use a variety of sensing elements such as diaphragms, bellows, bourdon tubes, or pistons. In most cases, the movement of these sensors, caused by pressure fluctuation, is transferred to a set of electrical contacts to open or close a circuit. Normal status of a switch is the resting state. A pressure switch will be in its “normal” status when it senses low or minimum pressure. For a pressure switch, “normal” status is any fluid pressure below the trip threshold of the switch.

One of the earliest and most common designs of pressure switch was the bourdon tube pressure sensor accompanied by a mercury switch. A mercury switch is a position sensitive glass bulb containing mercury that flows over, or away from, the electrical contacts. When pressure is applied, the bourdon tube attempts to straighten, and moves enough to slightly tilt the mercury switch. Many of these kind of pressure switches were sold on steam boilers, and while they became a de facto standard, they were sensitive to vibration and breakage of the mercury bulb.

electrical switch contacts
NO vs. NC electrical switch contacts.
The most common electrical switch used in pressure switches are "microswitch" type. These are also called "snap switches" because they are actuated by very little physical force, through the use of a tipping-point mechanism. These type of switches offer reliability and repeatability. They also are available in many different voltages and current ratings

One of the criteria of any pressure switch is the deadband or (reset pressure differential). This setting determines the amount of pressure change required to reset the switch to its normal state after it has tripped.  The “differential” pressure of a pressure switch should not to be confused with differential pressure switch, which actually measures the difference in pressure between two separate pressure ports.

When selecting pressure switches you must consider the electrical requirements (volts, amps, AC or DC), the area classification (hazardous, non-hazardous, general purpose, water-tight), pressure sensing range, body materials that will be exposed to ambient contaminants, and wetted materials (parts that are exposed to the process media).

It's always a good idea to discuss your application with an expert before specifying or installing a pressure switch. You'll end up saving time and money, and ensure long, safe operation.

For more information on pressure switches, contact Miller Energy by visiting https://millerenergy.com or by calling one of these numbers: In New Jersey 908-755-6700. In Pennsylvania 610-363-6200.