Industrial Electronics

#13 Robot Manipulator

Robotic arm

Robotic arm

Robots are computer-controlled devices which perform tasks usually done by humans.  An industrial robot is comprised of a robot manipulator, power supply, and controllers. Robotic manipulators can be divided into two sections, each with a different function:

  • Arm and Body – The arm and body of a robot are used to move and position parts or tools within a work envelope. They are formed from three joints connected by large links.
  • Wrist – The wrist is used to orient the parts or tools at the work location. It consists of two or three
    compact joints.

Robot manipulators are created from a sequence of link and joint combinations. The links are the rigid members connecting the joints, or axes. The axes are the movable components of the robotic manipulator that cause relative motion between adjoining links. The mechanical joints used to construct the robotic arm manipulator consist of five principal types. Two of the joints are linear, in which the relative motion between adjacent links is non-rotational, and three are rotary types, in which the relative motion involves rotation between links.

The arm-and-body section of robotic manipulators is based on one of four configurations. Each of these anatomies provides a different work envelope and is suited for different applications.

  • Gantry – These robots have linear joints and are mounted overhead. They are also called Cartesian and rectilinear robots. 
  • Cylindrical – Named for the shape of its work envelope, cylindrical anatomy robots are fashioned from linear joints that connect to a rotary base joint.   
  • Polar – The base joint of a polar robot allows for twisting and the joints are a combination of rotary and linear types. The work space created by this configuration is spherical. 
  • Jointed-Arm – This is the most popular industrial robotic configuration. The arm connects with a twisting joint, and the links within it are connected with rotary joints. It is also called an articulated robot.

The basic  industrial robot in wide use today is an arm or manipulator which moves to perform industrial operations. Tasks are specialized and vary tremendously. They include :

–        Handling                : loading and unloading components into machines

–        Processing             : machining, drilling, painting and coating

–        Assembling           : placing and locating a part in another compartment

–        Dismantling          : breaking down an object into its component parts

–        Welding                  : assembling objects permanently by arc welding or spot welding

–        Transporting       : moving material and parts

–        Painting                 : spray painting parts

–        Hazardous tasks : operating under high levels of heat, dust, radioactivity, noise, and noxious odors.

Source :

–        Robots web. “What is Robot Manipulator?”. 24 Mei 2014. http://www.robots.com/faq/show/what-is-a-robot-manipulator

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 389.

–        Picture : http://reset.etsii.upm.es/en/uploads/pool__projects_robotic-arm_robotic_arm.jpg/

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#12 The ON-Delay Timer (TON)

In this article will be explained about the on-delay timer (TON), before we know about TON, first it is better if we know about the timers. Timers are used to activate or de-activate a device after preset interval of time. PLC timers provide the same function as mechanical and electronic timing relays. There are three different timers, which are the on-delay timer (TON), the off-delay timer (TOF), and the retentive timer on (RTO). And there are two methods used to represent a timer instruction within a PLC’s logic ladder program, which are relay coil and block format.

The on-delay timer (TON) is the most commonly used timer. The on-delay timer operates so that when the rung containing the timer is true, the timer time-out period commences. At the end of the timer time-out period, an output is made active. The timed output becomes active sometime after the timer becomes active, hence the timer is said to have an ON delay.

The timer instruction consits of three data table words, such as the control word, the preset word, and the accumulated word.

1. Control word

The control word uses three bits, which are :

a. The Enable Bit (EN)

The enable bit is true (has status of 1) whenever the timer insstruction is true. When the timer instruction is false, the enable bit is false (has status 0).

b. The Timer-Timing Bit (TT)

The timer-timing bit is true whenever the accumulated value of the timer is changing, which means the timer is timing. When the timer is not timing, the accumulated value is not changing, so the timer timing bit is false.

c. The Done Bit (DN)

The done bit changes state whenever the accumulated value reaches the preset value.

2. Preset word

The preset value is the set point of the timer, that is, the value up to which the timer will time.

3. Accumulated word

The accumulated value is the value that increments as the timer is timing. The accumulated value will stop incrementing when its value reaches the preset value.

The timer instruction requires you to enter a time base, which is either 1.0 or 0.01 for long short time delays. The actual preset time interval is the timer’s preset word. The actual accumulated time interval is the time base multiplied by the value stored in the timer’s accumulated word.

The timer is activated by closing the switch. We can see in below figure, the preset time for this timer is 10 s, at which time output D will be energized. When the switch is closed, the timer begins counting, and counts until the accumulated time is automatically reset to zero. This timer configuration is termed nonretentive since loss of power flow to the timer causes the timer instruction to reset. This timing operation is that of an ON-DELAY timer, since output D is switched on 10 s after switch has been actuated from the OFF to the ON position.

The timing diagram first shows the timer timing to 4 s and then going FALSE. The timer resets, and both the timer-timing bit and the enable bit go FALSE. The accumulated value also resets to 0. Input A then goes TRUE again and remains TRUE in excess of 10 s. When the accumulated value reaches 10 s, the done bit (DN) goes from FALSE to TRUE and the timer-timing bit (TT) goes from TRUE to FALSE. When input A goes FALSE, the timer instruction goes FALSE and also resets, at which time the control bits are all reset and the accumulated value resets to 0.

Ladder diagram in TON

Ladder diagram in TON

Timing Diagram in TON

Timing Diagram in TON

Source :

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 354-356.

 

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#11 Three Types of Industrial Processes

The types of processes carried out in modern manufacturing industries can be grouped into three general areas. In terms of the kind of operation that takes place, as :

  1. Continuous Process
Continuous Process

Continuous Process

A continuous process is one in which raw materials enter one end of the system and the finished product comes out the other end of the system. The process itself runs continuously. Once the process commences, it is continuous for a relatively long period of time. The time period may be measured in minutes, day, or even months, depending upon the process.

  1. Batch Production
Batch Process

Batch Process

In batch processing there is no flow of product material from one section of the process to another. Instead, a set amount of each of the inputs to the process is received in a batch, and then some operation is performed on the batch to produce a finished product or an intermediate product that needs further processing. The process is carried out, the finished product is stored, and another batch of product is produced. Each batch of product may be different.

Some process combine the features of the batch and continuous types. In such processes, several product materials are treated and stored in batch operation. Then these stored materials are drawn off as required into a continuous process. Many chemically based products are manufactured by using batch processes.

  1. Individual Products Production
Individual Product Production

Example of Individual Product Production

The individual product production process is the most common of all processing systems. With this manufacturing process, a series of operations produces a useful output product. The item being produced may be required to be bent, drilled, welded, and so on. The workpiece is normally a discrete part that must be handled on an individual basis.

In moderen automated industrial plan, the operator merely sets up the operation and initiates a start, and the operations of the machine are accomplished automatically. These automatic machines and processes were developed to mass-produce products, control very complex operations, or to operate machines accurately for long periods of time. They replaced much human decision, intervention, and observation.

 

Source :

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 304-305.

–        Picture :

o   http://www.robots.com/images/robots/dsc_0039-10-27-06_3.jpg

o   http://rasmusson.files.wordpress.com/2008/04/batch1.jpg?w=300&h=186

o   http://www.pavloschemicals.com/images/metfloc2-1.gif

 

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#10 Three Basic Types of Temperature Mode Control

Temperature Controller

Temperature Controller

In this article will be explain an overview of commonly used industrial types of control function, it is temperature control. For more specific this article will present three basic types of temperature mode control. Temperature control may be used to maintain a specified temperature within a process or ti protect against overtemperature conditions.

A temperature controller is used to accurately control process temperature without extensive operator involvement. The controller accepts a temperature sensor such as a thermocouple or RTD as input and compares the actual temperature to the desired control temperature, or set point, and provides an output to control element.

Thermocouple is the junction of two dissmilar metals and has a voltage output proportional to the difference in temperature between the hot junction and the lead wires (cold junction).

There are three basic types of temperature mode control, namely :

  1. ON/OFF Temperature Control
On-off Control Diagram

On-off Control Graph

With ON/OFF Temperature Control, the output turns on when the temperature falls below the set point and turns off when the temperature reaches the set point. Control is simple, but overshoot and cycling about the set point can be disadvantageous in some processes. ON/OFF Temperature Control is usually used where a precise control is not necessary, in systems which cannot handle the energy being turned on and off frequently, where the mass of the system is great that temperatures change extremely slowly, or for temperature alarm.

  1. Proportional Temperature Control
Proportional Graph

Proportional Graph

Proportional controls are designed to eliminate the cycling associated with ON/OFF control. A proportional controller decreases the average power being supplied to the heater as the temperature approaches set point. This has the effect of slowing down the heater, so that it will not overshoot the set point but will approach the set point and maintain a stable temperature. Depending upon the process and the precision required, either a simple proportional control or one with PID may be required.

  1. PID Temperature Control
PID control graph

PID control graph

A PID, or three-mode controller, combines the proportional, integral (reset) and derivative (rate) actions, and is ussualy required for tight control of temperature-sensitive applications. The outputs turn on and off in proportion to temperature deviation from the set point. The rate function (derivative action) shortens the time it takes the temperature to stabilaze near the set point. The reset function (integral action) eliminates any offsets from the temperature set point.

Source :

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 283-284.

–        Picture :

o   http://img.getit.in/KT02DJ3I1temperature_controller.jpg

o   http://www.coulton.com/res/on_off_control.png

o   http://www.globalspec.com/ImageRepository/LearnMore/20127/Derivative%20Controlf33d02a7a8b14c83bea54ae58d67cc19.png

o   http://www.coulton.com/res/pid_control_graph.png

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#9 Part-Winding Starters

Part Winding Starters

Part Winding Starters

Part winding motors are similar in construction to standard squirrel cage motors. However, part winding motors have two identical windings that may be connected to the power supply in sequence to produce reduced starting current and reduced starting torque. These motor windings are intended to operate in parallel. Because only half of the windings are connected to the supply lines at startup, the method is described as part winding. (Many, but not all, dual-voltage, 230/460-volt motors are suitable for part winding starting at 230 volts.) By bringing out leads from each winding, the motor manufacturer enables the windings to be connected in parallel, external to the motor, with the starter.

Part winding starters are sometimes used on motors would for dual voltage operation, such as a 230/460  V motor. These motors have two sets of windings connected in series for high-voltage operation. When used on the lower voltage, they can be started by first energizing only one winding, limiting starting current and torque to approximately one-half of full the voltage values. The second winding is then connected normally, once the motor nears operating speed about 2 s later.

Part winding starters are designed to be used with squirrel cage motors having two separate and parallel stator windings. In the part winding motor, these windings may be Y connected or delta connected, depending on the motor design.

Part winding starters are not suitable for use with delta-wound and dual-voltage motors.

Part winding motors are used to drive centrifugal loads such as fans, blowers, or centrifugal pumps. They are also used for other loads where a reduced starting torque is necessary.

This type of motor is also used where the full voltage starting current will produce objectionable voltage drops in the distribution feeders or where power company restrictions require a reduced starting current. Using a part winding starter to start a motor does not necessarily reduce the maximum starting current. Instead, incremental starting is obtained. Neither one of the two windings has the thermal capacity to operate alone for more than a few seconds. Therefore, unless the motor accelerates to practically full speed on the one winding, the TOTAL cur rent drawn may approach that of line voltage starting.

This type of starting has many applications in air-conditioning systems. This is due to the increased capacity built into these systems and the necessity of limiting both the current and torque on starting.

Source   :

–        Industrial electronics web. “Part Winding Motor Starters–AC Reduced Voltage Starters”. 20 Mei 2014. http://www.industrial-electronics.com/Motor_Control_5-28.html

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 246.

–        Picture : http://constructionmanuals.tpub.com/14026/img/14026_252_1.jpg

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#8 Solid-State Contactor

Solid-State Contactor

Solid-State Contactor

Solid-state switching means interruption of power by nonmechanical electronic means. A solid-state contactor is a power-switching device designed to replace magnetic contactor for applications involving both resistive and inductive loads.

Solid-state three-phase contactors are especially suited to high-cycling applications owing to the absence of arc-producing air gap contacts. Size range from 10 to 600 A, with input voltage from 240 to 550 Vac. Solid-state contactors now replace three-pole electromechanical contactors in industrial furnaces and ovens, mining and materials handling, and other industrial heating applications.

Silicon-controlled rectifiers (SCRs) enable reliable control of electric power from 1 kW to 1000 kW for most types of resistance heaters, motors, and other inductive loadds. It consists of a specially treated silicon disc enclosed in a plastic or ceramic housing with metal power leads arranged for the anode and cathode connections and a smaller tab or wire for the gate connection. The SCR, like a contact, is in either the ON state (closed contact) or the OFF state (open contact). The SCR is analogous to a “latched relay” circuit. Once the SCR is triggered, it will stay ON until its current decreases to zero. When current through the SCR stops, the “SCR switch” will open and stay open until retriggered.

In contrast to a magnetic contactor, an electronic contactor is absolutely silent, and its “contacts” never wear out. Inductive loads and voltage transients are both seen as problem areas in solid-state ac control includes a resistor and capacitor in series connected in parallel to each power pole. These “RC” or “snubber” networks divert the charging current from the SCRs and help prevent unwanted turn-on.

All silicon semiconductors, when in the ON state, still have a small voltage drop accross the junction of 1 to 2 V. The resultant 1 to 2 W of heat per conducted ampere through the device must be removed to the outside environment. Properly designed heat sinks acccomplish this normally by conduction or convection heat transfer to maintain the silicon below its maximum temperature level.

The abrupt switching of the SCRs from the blocking state to the conducting state, particularly ath higher current levels, may sometimes cause objectionable transients on the power line and create radio frequency interference (RFI). Zero-fired control refers to turning ON the SCRs at the zero voltage crossing for full cycles, applying full power or no power with the proportion of full cycles, or determining the resulting power to the load. This is sometimes called integral cycle mode or “burst firing.” The result is eliminaton of power line disturbances and RFI.

Source :

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 231-233.

–        Picture : http://www.power-io.com/gifs/dda5075100.gif

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#7 Solid-State Relays

Solid-State Relay

Solid-State Relay

A solid state relay (SSR) is just what it sounds like; an IC that acts like a mechanical relay. They allow you to control high-voltage AC loads from lower voltage DC control circuitry. Solid state relays, have several advantages over mechanical relays. One such advantage is that they can be switched by a much lower voltage and at a much lower current than most mechanical relays. Also, because there’s no moving contacts, solid state relays can be switched much faster and for much longer periods without wearing out.

They accomplish this by using infrared light as the ‘contact,’ a solid-state relay is really just an IR LED and a phototriac sealed up into a little box. Thanks to the fact that the two sides of the relay are photo-coupled, you can rely on the same type of electrical isolation as in mechanical relays.

SSRs do not have actual coils and contacts. Instead, they use semiconductor switching devices such as bipolar transistor, MOSFETs, silicon-controlled rectifiers (SCRs), or triacs. The solid-state relay has no moving parts, it is resistant to shock and vibration, and it is sealed against dirt and moisture.

SSRs can be used to control ac or dc loads. If the relay is designed to control an ac load, a triac is used to connect the load to the line. Solid-state relays intended for use as dc controllers have a power transistor, rather than a triac, connected to the load circuit. When the input voltage turns on the LED, a photodetector connected to the base of the transistor turns the transistor ON and connects the load to the line.

The control voltage for SSRs can be direct current or alternating current and usually ranges from 3 to 32 V for the dc versions and 80 to 280 V for ac versions. Maximum load circuit amps of up to 50 A are possible at input line voltage ratings of 120,240, and 480 Vac. In most applications, SSRs are used to interface between a low-voltage control circuit and a higher ac line voltage.

Many SSRs used to control ac loads have a feature known as zero switching. Zero switching ensures that the relay is turned ON or OFF at the beginning of the ac voltage wave at the zero crossover point. Zero voltage switching is often needed to reduce in-rush current and radio frequency interference (RFI).

The SSR has several advantages over the EMR, such as :

–        The SSR is more reliable and has no longer life because it has no moving parts.

–        It is  compatible with transistor and IC circuitry and does not generate as much elecctromagnetic interference.

–        The SSR is more resistant to shock and vibration, has much faster response time, and does not exhibit contact bounce.

The SSRs do have some disadvantages, such as :

–        The SSR contains semiconductors that are susceptible to damage from voltage and current spikes.

–        Unlike the EMR contacts, the SSR switching semiconductor has a significant ON-state resistance and OFF-state leakage current.

Source :

–        Sparkfun web. “Solid State Relay – 8A”. 18 Mei 2014. https://www.sparkfun.com/products/10636.

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 205-207.

–        Picture : http://www.china-relay.com/images/solid-state-relays-SSRs-01.jpg

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#6 Compound Wound DC Generator

In series wound generators, the output voltage is directly proportional with load current. In shunt wound generators, output voltage is inversely proportional with load current. A combination of these two types of generators can overcome the disadvantages of both. This combination of windings is called compound wound DC generator.

Compound wound generators have both series field winding and shunt field winding. One winding is placed in series with the armature and the other is placed in parallel with the armature. This type of DC generators may be of two types- short shunt compound wound generator and long shunt compound wound generator.

  1. Short Shunt Compound Wound DC Generator

The generators in which only shunt field winding is in parallel with the armature winding as shown in figure.

Short-Shunt-Compound-wound-generator

Series field current, Isc = IL
Shunt field current, Ish = (V+Isc Rsc)/Rsh
Armature current, Ia = Ish + IL
Voltage across the load, V = Eg – Ia Ra – Isc Rsc
Power generated, Pg = Eg×Ia
Power delivered to the load, PL=V×IL

  1. Long Shunt Compound Wound DC Generator

The generators in which shunt field winding is in parallel with both series field and armature winding as shown in figure.

Long-Shunt-Compound-wound-generator

Shunt field current, Ish=V/Rsh
Armature current, Ia= series field current, Isc= IL+Ish
Voltage across the load, V=Eg-Ia Ra-Isc Rsc=Eg-Ia (Ra+Rsc) [∴Ia=Ics]
Power generated, Pg= Eg×Ia
Power delivered to the load, PL=V×IL
In a compound wound generator, the shunt field is stronger than the series field. When the series field assists the shunt field, generator is said to be commutatively compound wound. On the other hand if series field opposes the shunt field, the generator is said to be differentially compound wound.

commulatively-differentially-compound

Source :

–        Electrical4u web. “Types of DC Generators”. 18 Mei 2014. http://www.electrical4u.com/types-of-dc-generators/

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#5 Zener Diodes

Zener Diode

Zener Diode

Zener diodes are semiconductor diodes which have been manufactured to have their reverse breakdown occur at a specific, well-defined voltage (its “Zener voltage”), and that are designed such that they can be operated be operated continuously in that breakdown mode. The zener diode is like a rectifying diode in that it allows current to flow in the foward direction. It differs from a rectifying diode, however, in that its reverse-direction breakdown voltage is much lower than that of an ordinary rectifying diode. It is very heavily doped during manufacture. The large number of extra current carriers allows the zener diode to conduct current un the reverse direction. This reverse bias current would destroy a normal diode, but the zener is made to operatet this way. The specified zener voltage rating of a zener diode indicates the voltage at which the diode begins to conduct when reverse biased. Commonly available Zener diodes are available with breakdown voltages (“Zener voltages”) anywhere from 1.8 to 200 V.

normal diode current flowBackward current flow

The schematic symbol for a Zener diode is shown above– it is very similar to that of a regular diode, but with bent edges on the bar. The Zener still conducts electricity in the forward direction like any other diode, but also conducts in the reverse direction, if the voltage applied is reversed and larger than the Zener breakdown voltage.

Zener Circuit

Zener Circuit

A typical application might be as above: A 10 V Zener diode (type 1N4740) is placed in series with a resistor and a fixed 12 V power supply. The resistor value is chosen such that several mA flow through it and through the Zener, keeping it in its breakdown region. In the circuit above, there is 10 V across the Zener diode, and 2 V across the resistor. With 2 V across a 400 ohm resistor, the current through that resistor (and the diode, in series) is 5 mA.

Source :

–        Evil mad scientist web. “Basic : Introduction to Zener Diodes”. 24 May 2014. http://www.evilmadscientist.com/2012/basics-introduction-to-zener-diodes/

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 131.

–        Picture : http://upload.wikimedia.org/wikipedia/commons/d/df/Zener_Diode.jpg

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#4 Thermostat

Nest Cooling

Nest Cooling

A thermostat is a device that is used to control a heating or cooling system so that it maintains a certain temperature or keeps the temperature within a certain range. In a home, for example, this device can automatically turn on the heating system when the temperature in the home drops or turn on the air conditioning when it gets too hot. As the warm or cool air fills the room and the desired temperature is achieved, the device then turns off the system. There are two main types of thermostats: mechanical and digital.

Mechanical Thermostats

Roundstat

Roundstat

A mechanical thermostat uses physical means to gauge the air temperature and activate a switch that turns on a heating or cooling system on turns it off. There are several types of sensor technology that can be used in mechanical thermostats, such as bimetallic strips, wax pellets, bulbs filled with gas or tubes filled with air. Each of these types of sensors will react to changes in temperature, such as by expanding or contracting, and will trigger the proper switch to raise or lower the temperature. Bulbs filled with mercury were once commonly used in thermostats, but its use has been discontinued or outlawed in many places because of the dangers of mercury.

The most common of these technologies in home thermostats is the bimetallic strip. This technology uses two thin strips of different metals — such as copper and iron, copper and steel and brass and steel — bonded together and rolled into a coil. As the temperature changes, the different metals expand or contract at different rates, causing the strip to bend. When the strip bends enough to touch an electrical contact and complete an electrical circuit, it turns on the heating or cooling system. If the temperature changes enough to unbend the strip, contact is lost, and the system turns off.

Digital Thermostats

Digital Thermostat

Digital Thermostat

Based on the temperatures read by the electronic sensors, these devices turn on or off the cooling or heating systems as needed. A digital thermostat usually requires one or more batteries for power. Buttons and switches allow the user to control the settings, and a display screen shows the settings as well as the current temperature.

Setting a Thermostat

To set a mechanical thermostat, the user typically must turn a dial or move a lever. One common type of mechanical thermostat has a dial that has a range of temperatures printed on it, and the user simply turns the dial until a small arrow or line is on the preferred temperature. Another type is rectangular and has two levers that allow the user to set a minimum temperature and a maximum temperature. These thermostats often also have switches that allow the user to turn on or off the heating or cooling system as well as anyventilation fans that might be part of the system.

When setting digital thermostats, in most cases, the users simply look at the display screens and push buttons to input the desired settings. Some newer models feature touch screens instead of separate buttons and display screens. For a programmable model, the user could choose to have different setting for certain times, such as when the home’s residents are sleeping, when they are first waking up or when they are away at work or school. Programmable settings not only can make a home more comfortable, they also can conserve energy by keeping the heating or cooling system from turning on or off unnecessarily, such as when nobody is home. Depending on the model, these programmed times might be when the device begins adjusting the temperature, or the device might begin working earlier so that the desired temperature is achieved at the programmed time.

 

Source:

–        Wisegeek web. “How Does a Thermostat Work?”. 17 Mei 2014. http://www.wisegeek.com/how-does-a-thermostat-work.htm

–        Picture : http://larryfire.files.wordpress.com/2011/10/nest_cooling.jpg Nest Learning Thermostat.

–        http://valleyservices.files.wordpress.com/2009/12/roundstat.jpg Classic round Honeywell thermostat.

–        http://www.emersonclimate.com/en-us/Products/Thermostats/PublishingImages/thermostats_hi_res/1F97_0671_Emerson_clip.jpg  Digital Thermostat.

 

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