l205en(Temperature Regulators)

Part

2Se

lf-op

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gula

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Temperature Regulators

Technical Information

2

Part 1: Fundamentals

Part 2: Self-operated Regulators

Part 3: Control Valves

Part 4: Communication

Part 5: Building Automation

Part 6: Process Automation

Should you have any further questions or suggestions, pleasedo not hesitate to contact us:

SAMSON AG Phone (+49 69) 4 00 94 67V74 / Schulung Telefax (+49 69) 4 00 97 16Weismüllerstraße 3 E-Mail: [email protected] Frankfurt Internet: http://www.samson.de

Technical Information

Temperature Regulators

Temperature regulators . . . . . . . . . . . . . . . . . . . . . . . . 5

Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Liquid expansion principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Sensor volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Filling medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Adsorption principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Vapor pressure principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

How the sensor design influences the dynamic behavior . . . . . . . . 13

Types of bulb sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Set point adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Excess temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Mounting position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Dynamic behavior of sensors . . . . . . . . . . . . . . . . . . . . . 18

Valves and their applications . . . . . . . . . . . . . . . . . . . . . 21

Force-balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Globe valves in cooling service . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Three-way valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Safety engineering and combination technology. . . . . . . . . . . . . . . 28

Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Appendix A1: Additional literature . . . . . . . . . . . . . . . . . . 31

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Self-operated Regulators ⋅ Temperature Regulators

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Temperature regulators

Self-operated temperature regulators belong to the group of direct acting re-gulators which require no external source for operation. Their characteristicfeature is their compact design, including a sensor, a valve and a capillarytube. Their simple operating principle is based on fundamental mechanical,physical and thermodynamic laws. A temperature control loop with a heatexchanger is shown in Fig.1. When the water has left the heat exchangerand circulates in the domestic hot water loop, its temperature must be keptconstant. In the heating loop, a heat transfer medium, e.g. hot water, circula-tes through the heat exchanger and transfers part of its heat to the domestichot water loop. If we assume that the temperature of the hot water remainsconstant, the transferred heat quantity depends on the flow rate. The flow ofhot water is adjusted by the self-operated regulator.

The sensor measures the temperature of the medium to be controlled andconverts the measured value into a pressure signal which is used as outputvariable. The sensor output signal is transmitted via the capillary tube to theoperating element where it is converted into a travel which results in a chan-ge of the plug position. Temperature regulators obtain their actuating powerfrom the medium to be controlled, so they do not need supply lines or auxilia-ry devices. This is the most important benefit of self-operated regulators. Theykeep costs low, while exhibiting high operational reliability.

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Fig. 1: Temperature control loop with heat exchanger

temperaturesensor

self-operatedregulator

heat exchanger

heating loop domestic hotwater loop

temperature

control loop

Sensors

Sensors are used to measure the temperature of the medium to be controlled.A good sensor must fulfill two important requirements. It must respond quick-ly to temperature changes and provide accurate values of variables thatchange over time. The self-operated regulator measures variables accordingto the three following principles:

4 liquid expansion

4adsorption

4vapor pressure

These principles utilize the change in volume, in structure or the conversion ofa matter�s state of aggregation.

Liquid expansion principle

When measuring the expansion of a liquid, the quality of the results dependsto a great extent on two factors: the sensor volume and the specific heat ca-pacity of the filling medium.

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h

h 2.0

d1

V1

V1.0

d2

V2.0

V2

1

3

2

��

��

h 1h 1

.0h 2

Fig. 2: Expansion of a liquid in a cylinder

h1 < h2

h1.0 < h2.0

V1=V2

V1.0=V2.0

1: sensor

2: operating element

3: cylinder

sensor

measurement is based

on three methods

� Sensor volume

Solids, gases and almost all liquids expand when the temperature increases.This physical principle of expansion is utilized by thermometers. An increasein temperature causes the liquid level in a capillary to rise. This level is indica-ted on a scale.

A sensor operating on the liquid expansion principle is shown in Fig. 2. Theliquid expands in the cylinder when the temperature rises. As the wall of thecylinder prevents lateral expansion, the liquid expands only in the axial di-rection, pushing the piston and the connected pin upward.

The increase in volume can be calculated as follows:

The expansion of the filling medium is determined by two factors�the speci-fic coefficient of expansion γ which depends on the type of fluid used and thechange in temperature ∆T.

The height of the pin protruding from the cylinder is a measure for the expan-sion and represents a function of the temperature h=f(T). To achieve a parti-cular travel of the pin ∆h, the shape of the operating element must beconsidered and adapted as required. Generally, small sensor volumes yieldlarger travels than large volumes (Fig. 2). In instrumentation, small workingcylinder areas or narrower working cylinders are preferred since the measu-ring span is better represented when the pin travel is large. In this way, moreaccurate measurement results are obtained. However, a disadvantage ofsmall-volume sensors is the low power transmission. A movement of the val-ve, though, always requires an (actuating) force. When sizing a sensor, acompromise must be found between the change in travel and temperature aswell as the increase in force.

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expansion in the

cylinder

∆V = V0 γ ∆T

expansion as a function

of temperature

� Filling medium

To quickly obtain accurate measurements, the quantity of heat a sensor mustabsorb and release should be as low as possible. This can be achieved eitherby keeping the volume or the mass low, or by choosing a filling fluid with alow specific heat capacity. The quantity of heat stored in the fluid calculatesas follows:

cp is the specific heat capacity, m the mass and ∆T the change in temperaturein °C. Note that the specific heat capacity is not constant, but changes withthe temperature.

Due to its high specific heat capacity, water is not suitable as filling medium.It has yet another disadvantage: With the exception of water, all liquids ex-pand continuously with increasing temperatures and condense when thetemperatures fall. Water, however, reaches its highest density at 4 °C andexpands at higher as well as lower temperatures. Therefore, the temperaturemeasured in these ranges would not be clear.

SAMSON temperature sensors use low-viscous, synthetic oil as filling me-dium. This liquid is harmless, i.e. it endangers neither health nor environ-ment. It can be discharged with the waste water if leakage occurs (waterdanger class 0). Formerly used silicone oils were not accepted by the auto-motive industry since silicone oils cause wetting problems with water-basedlacquer.

Apart from liquids, resins and elastomers can also be used as filling fluid.

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W = cp m ∆T

water not suitable as

filling medium

small heat capacity

enables fast-

responding sensors

Adsorption principle

The adsorption principle is based on a physical method. The temperaturesensor contains activated carbon and carbon dioxide. When the sensor isheated by the medium to be measured, the activated carbon releases CO2

molecules. The pressure inside the sensor increases (Fig. 3), representing asignificant value for each temperature value. When the internal pressure istransmitted via a control line to the operating bellows, the valve position ischanged with respect to the temperature.

The most important benefit of the adsorption principle is its good adaptationto the respective application. The measuring span of an adsorption sensorcan be set in two ways:

4different types of activated carbon and gases yield different pres-sure-temperature curves;

4varied filling conditions yield different operating ranges. Four overlap-ping set point ranges are available, covering the range from 0 to 150 °C.

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CO2 CO2

Fig. 3: CO2 molecules depositing on activated carbon

activated carbon

T1, p1 T1 > T2

p1 > p2

T2, p2

activated carbon

releases CO2 molecules

flexible application...

These thermostats produce a smaller thrust, though, than sensors based onthe liquid-expansion or vapor-pressure principle.

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p

p

1

2

1

2

3

8

7

9

4

10

11

p

t

5

Fig. 4: Temperature regulator based on the adsorption principle

1 Valve body2 Valve seat3 Plug4 Plug stem5 Valve spring7 Positioning spring8 Set point adjuster9 Operating bellows10Capillary tube11Temperature sensor

� but small

thrust

Vapor pressure principle

The vapor pressure principle is based on a thermodynamic method. When aliquid is subjected to heat, it begins to boil at a certain temperature and ste-am is generated.

The boiling temperature, however, depends on the prevailing pressure. Thelower the pressure, the lower the temperature at which the liquid starts toboil.

Example: In an open vessel, water boils at 100 °C. The boiling temperaturein a pressure cooker, however, is considerably higher because the pressurecreated in the airtight cooker is much higher.

The steam pressure curves of hydrocarbons are plotted in Fig. 5. When thetemperature of the medium to be measured increases, the boiling pressure inthe closed sensor system increases as well, following the rising steam curve.

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100

10

1

0.1-50 0 50 100 150 200

Fig. 5: Steam pressure curves of hydrocarbons

n-butanepropane

n-pentane

n-heptane

p v[b

ar]

T [°C]

sensor system utilizes

steam pressure curve

Depending on the measured temperature, a significant pressure is created inthe sensor. The internal sensor pressure acts on a bellows in the thermostat,generating a thrust. The filling medium in sensors for self-operated regula-tors often is a mixture of hydrocarbon compounds (HC-compounds).

The maximum ambient temperature must be minimum 15 K lower than theset point to prevent the filling medium from vaporizing in the control line.

The basic properties of the different measurement methods are compared inthe following table.

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Sensorliquidexpansion

adsorption vapor pressure

thrust strong weak medium

expansionbehavior

linear linear not linear

excess. temp.safety

low high medium

mount. position any any defined

Table 1: Properties of different sensor systems

How the sensor design influencesthe dynamic behavior

Types of bulb sensors

Bulb sensors are in direct contact with the medium. The resulting heat ex-change is characterized by the heat transfer coefficient.

The heat transfer coefficients of liquids are remarkably higher than those ofgases. Temperature changes of a liquid act therefore faster on the sensorcase, the filling medium and finally the valve position. When sizing the tem-perature sensor, the surface provided for heat transfer must be as large aspossible. While the cylindrical surface of a bulb sensor is sufficient for mea-

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Fig. 6: Unit step response of a bulb sensor and a four-bulb sensor

water

air

bulb sensor

water

air

four-bulbsensor

200 400 600 800

1

Y

Y

1

200 400 600 800

t [s]

t [s]

0.6

0.2

0.6

0.2

sensors require large

heat transfer surfaces

suring water and other liquids, gases require a specially manufacturedfour-bulb sensor. In this sensor, the ratio between the sensor surface and thevolume of the filling medium is larger than that of the bulb sensor. Fig. 6 com-pares the unit step response of a bulb sensor with that of a four-bulb sensorafter they have been immersed into warm circulating water and into an airduct. The temperature difference is so big that the pin passes through its enti-re travel. Particularly in the air duct, the larger sensor volume proves favor-able. Compared to the four-bulb sensor, the pin of the bulb sensor requiresalmost three to four times as much time to reach its final travel.

Set point adjustment

Self-operated regulators usually exhibit proportional control action (P regu-lators). In the case of self-operated temperature regulators, the proportionalaction causes the valve travel h to change proportionally with the measuredtemperature T. The proportional-action coefficient is Kp (formerly: proportio-nal band Xp; Xp = 100 %/Kp). The following equation describes the controlaction for temperature regulators.

As described in the Control Engineering Fundamentals (see also Lit. [2]), Pregulators have a steady-state error. When the steady-state error is to bekept small, a large proportional-action coefficient is required (small propor-tional band). This means for the temperature regulator that a large travelmust be achieved at a small ∆T. The measuring span of the sensor becomesaccordingly smaller.

However, narrow measuring spans are an obstacle to the universal applica-tion of sensors. Therefore, the temperature regulator is equipped with a setpoint adjuster.

Example: In systems with volume changes, an externally adjustable pistoncan be moved to change the volume of the system. When the piston is pushedinto the right cylinder, the pin in the operating element is lifted, providing the

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large travel

at small ∆T

∆h = Kp · ∆T

control action of

self-operated regulators

universal

application requires

set point adjuster

universal

application requires

set point adjuster

required volume. As a result of the changed pin position, the travel positionof the valve is changed, too (Fig.7).

Excess temperature

When the temperature reaches the upper limit of the set point range (closingtemperature), the pin is fully extended. The valve is in its end position. Whenthe temperature rises above this value, the liquid in the sensor cannot expandfurther. If no equalizing volume is provided, the rising internal pressure willdamage the sensor. To prevent this, a pressure relief fitting is installed (Fig.8).

When excess temperatures occur, the rising filling pressure acts on the pistonbottom and pushes the piston out of the sensor against the force of the excesstemperature spring. This increases the sensor volume. Excess temperaturesonly occur under the influence of externally supplied energy, in case of a de-fective valve (the valve does not completely close) or with extremely oversi-zed valves. Decreasing the set point will not help, since the valve is alreadyclosed in this state. In the end, decreasing the set point results in a defectivedevice.

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Fig. 7: Example: Set point adjustment at temperature sensor (system basedon change in volume)

pin

operatingelement

piston

sensor protected

against excess

temperature

Mounting position

A prerequisite for the proper functioning of temperature control systems isthe optimum location of the sensor. It should be totally immersed in the medi-um to be measured (see Fig. 9).

Another important requirement is that the sensor measures nearly withoutdead time. Dead times occur, for example, in a heating system when the sen-sor is not located directly at the heat source, e.g. the heat exchanger, but faraway in the heating pipe. In this case, temperature changes are measuredwith delay. These dead times can cause the system to oscillate and can trig-ger the safety mechanisms due to excess temperatures created. In addition tothe aspects to be considered in sensor positioning, the dynamic behavior ofthe sensor also plays an important role for the heat transfer.

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Fig. 8: Excess temperature protection of the sensor

connection tooperating

element

set point adjuster

excess temperaturespring

gasket

piston

dead times must be

avoided

wrong position affects

measurement results

Ad a, b)The sensor�s entire length is fully immersed in the medium

Ad c, d)The sensor is only partially immersed in the medium

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Fig. 9: Sensor locations

a) correct b) correct

c) permissible if itcannot be avoided

d) incorrect

Dynamic behavior of sensors

The dynamic behavior of a self-operated regulator depends on the dynamicbehavior of its sensor. The dynamic behavior is characterized by the timeconstant τ. The constant describes the time the pin needs to reach approxi-mately 63 percent of the new operating point when forced by a step changein temperature.

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t[s]

sensorC

B

A

x 0.63

1

0.2

20 100806040τA τCτB

sensor withthermowell

x

t[s]

C

B

20 806040

1

0.6

0.2

x

120

120100

τB τC

( ) ( )( )

x tx

e

for txx

t

max

max

: . %

= −

= ⇒ = =

−1

0 63 63

τ

ττ

When looking at the sensor from the viewpoint of control engineering, thesensor can be regarded as energy store. Its dynamic behavior can be descri-bed by means of an exponential function using the time constant T1 = τ(first-order delay). When mounting a thermowell (see chapter Accessories),another energy store is added to the system. Hence, a second-order system iscreated. To describe such a system, the time constant Tu and the build-up timeTg can be used. For further details, please refer to the Technical InformationL102 EN.

As can be seen in Fig. 10, small time constants are typical to fast-respondingsensors.

Table 2 lists the time constants of the different SAMSON sensors. Measure-ments were made in water. You can see from the table below that the use of athermowell causes long delays.

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Principle Type without thermowell with thermowell

liquid expansion 2231 70 120

2232 65 110

2233 25 --- 1)

2234 15 --- 1)

2235 10 --- 1)

2213 70 120

adsorption 2430 15 2) 30 3) 40 2) 80 3)

2430-L 8 --- 1)

2212 --- 1) 40

2439 --- 1) 40

vapor pressure 2430-3 3 --- 1)

2403 10 45

Table 2: Time constants in seconds1) not permissible 2) sensor diameter 9.5 mm 3) sensor diameter 16 mm

sensor and thermowell

both exhibit PT1 action

thermowells prolong

the response time

It practically eliminates the fast response times inherent to sensors, and theyare almost as �slow� as liquid-expansion sensors.

Standard materials for sensors and thermowells are usually copper or bron-ze because of their excellent conductivity. For corrosive media, stainless steelversions are used. When a stainless steel sensor is used, the time constantincreases by approximately ten percent compared to copper sensors. Withthermowells, the time constants of copper and stainless steel versions are ne-arly identical.

Thermowells are not suited to be used with sensors for air. Due to the specialsensor shape, a narrow air gap is formed between the thermowell and thesensor, which has an insulating effect. The time constant of an air sensor withthermowell would be much higher than that of a standard sensor with ther-mowell.

NOTE: In addition to the time constant τ, variables such as T0.5 (half-valueperiod) or T0.9 (90% value) are used to describe the dynamic behavior ofsensors. These values can be calculated for first-order systems using theequation below and the time constant τ:

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( )( )

x t x e

tx tx

tt

t

= −

= − −

⋅

= ⋅

−

max

max

.

.

( )

ln

.

1

1

0 70 5

0 9

τ

τ

τ= ⋅2 3. τ

sensor material:

bronze and copper

Valves and their applications

Force-balancing

The signal pressure of self-operated regulators is generated by the expansi-on of the filling medium in the operating element. To make the interaction ofthe different forces understandable, a valve balanced by a bellows is descri-bed in the following example (see also Technical Information L202EN).

The upstream pressure p1 and the downstram pressure p2 acting on the valveplug are balanced by the bellows. As a result, the actuating force FA is oppo-sed only by the pre-loaded spring FF (Fig. 11). Both forces are balanced in astate of equilibrium.

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spring and actuating

force are balanced in a

state of equilibrium

Fig. 11: Force balance after increase in temperature

FA1 FF1

T1 = constant

FA2 FF2

T2 = T1 + DT

The self-operated regulator is used to reduce or increase the flow rate whenthe temperature at the measuring point rises or falls.

The temperature is regulated as follows:

4When the medium heats up, e.g. due to a reduction of the flow rate, the fil-ling liquid in the operating element expands and exerts the actuating forceFA on the valve.

4The valve closes against the spring force FF, reducing the flow of the heat-ing medium.

4When the flow is reduced, the temperature falls until a new equilibrium offorces and, hence, a new valve position is reached.

NOTE: When sizing a system including a heat exchanger, the upstream tem-perature must be minimum 10 K above the set point temperature to ensuresafe closing of the valve.

Globe valves in cooling service

The globe valves described above close when the temperature at the sensorrises, hence, they are suitable for heating service. In cooling installations, ho-wever, a system is required that opens the valve with increasing temperatureto release the cooling medium.

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Fig. 12: Reversing device for globe valves in cooling service (valve is closed bythe spring force of the reversing device and opens when the temperature rises)

reversing device

changes operating

direction

connectionto operatingelement

valve

closing spring

This is achieved either by installing a reversing device between the 'normal'globe valve and the operating element (Fig. 12), or by changing theseat/plug position (Fig. 13).

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p p1 2

pt

Fig. 13: Temperature regulator with pressure balanced plug(valve opens when the temperature rises)

balancing bellows

plug

Three-way valves

Heating and cooling control systems require different valve styles. Globe val-ves control one flow to adjust the desired temperature. Three-way valves, onthe other hand, mix or divert two heat flows.

Three-way valves have three ports (A, B, AB), while globe valves have two.When no actuating force is exerted on the valve, a return spring ensures thatthe plug is firmly placed on one of the two seats.

In mixing valves (Fig. 14), the heating medium enters at port B via theseat/plug assembly and leaves through port AB. Port A is closed. When anactuating force acts on the plug stem, the valve moves towards its other endposition, reducing the flow through the inlet port B and opening the inlet portA.

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A AB

B

Fig. 14: Three-way mixing valve

medium flow through

mixing valves

The flow through diverting valves (Fig. 15) is quite different. Here, theprocess medium enters at port AB. The streams are diverted according to thevalve position and finally leave through the ports A and B.

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B

AAB

Fig. 15: Three-way diverting valve

medium flow through

diverting valves

The operating principle of the valves and their application in a heating and acooling system are illustrated in Figs. 16 and 17.

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Fig. 16: Example of a heating system

control task: constant temperature in the consumer loop

flow control diverting

valve closes

globe valve three-waymixing valve

three-waydiverting valve

A opensB closes

A closesB opens

when temperature increases

mixing

AB

B

A A

B

AB

heating system

Figs. 16 and 17 (heating/cooling) show typical installation examples wherethe valves can be installed either in the flow pipe or in the return pipe. In hea-ting systems with high temperatures and low pressures, cavitation can causeproblems, therefore the valve should be installed in the cooler return pipe.

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flow control diverting

valve opens

globe valvethree-waymixing valve

three-way di-verting valve

A opensB closes

A closesB opens

mixing

when temperature increases

A

B

AB

A

B

AB

control task: constant temperature in the consumer loop cooling system

installation of valves in

heating or cooling

systems

When engineering the heating or cooling installation, it must be ensured thatthe process medium flows in the opening direction of the plug of the mixingor diverting valve so that "vibrations" near the closing position are preven-ted. The small surface, the high velocity and the low pressure wouldotherwise cause the plug to be seized in the seat and released again whenthe flow is interrupted.

Safety engineering and combination technology

One important field of application for temperature regulators (TR) is in safetyengineering. The following safety equipment can be differentiated:

� Safety temperature monitor (STM)

The STM closes the valve in heating operation and opens it in cooling opera-tion when the limit value is exceeded or when the device is defective. Oncethe temperature lies within the limit value range again, the control function isautomatically reactivated.

� Safety temperature limiter (STL)

The STL closes the valve in heating operation, opens it in cooling operationand locks the valve when the limit value is exceeded or when the device is de-fective. Once the temperature lies within the limit value range again and af-ter mechanical unlocking (loading the closing spring), the control function isautomatically reactivated.

� Combination technology

STMs and STLs can, of course, be combined with other TRs. For reasons ofsafety, systems can also be equipped with a combination of STL and STM.

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Accessories

The following accessories are designed for use with temperature regulatorsand are available for different applications:

� Thermowells and flanges

Thermowells are used to protect the sensor from the medium. This is impor-tant, for instance, when chemically corrosive media would damage the sen-sor material. Thermowells can be additionally coated with PTFE forprotection.

Basically, sensor flanges can be designed with and without thermowells.Flanged thermowells are frequently used for high nominal pressure ratings(> PN 40).

Using thermowells has another big advantage: The process medium can re-main in the system when a sensor must be replaced.

� Distance pieces

Distance pieces are used to seal the valve/thermostat connection. At thesame time, they isolate the operating element of the thermostat from theprocess medium flowing through the valve.

� Double adapter

A double adapter enables the connection of additional controlled variables.In a heating system, for instance, a double adapter can be installed toregulate the return flow temperature limitation in addition to the main task ofregulating the desired heating temperature.

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� Extension pieces

For applications with heating media exceeding a temperature of 220 °C,extension pieces are used to prevent the heat from being radiated on theoperating element. Contrary to distance pieces, extension pieces do notrequire an internal seal, because they are not primarily used for the isolationof the sensor from the medium. In case special applications should require aseal, this seal can be integrated in the extension piece.

� Electric signal transmitter

Electric signal transmitters can be used to indicate different operating states.Depending on the application, information such as �Valve closed� or even�Safety temperature limiter triggered� could be of interest.

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Appendix A1:Additional literature

[1] Terminology and Symbols in Control EngineeringTechnical Information L101EN; SAMSON AG

[2] Controllers and Controlled SystemsTechnical Information L102EN; SAMSON AG

[3] Self-operated RegulatorsTechnical Information L202EN; SAMSON AG

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APP

ENDI

X

Figures

Fig. 1: Temperature control loop with heat exchanger . . . . . . . . . 5

Fig. 2: Expansion of a liquid in a cylinder . . . . . . . . . . . . . . . 6

Fig. 3: CO2 molecules depositing on activated carbon . . . . . . . . . 9

Fig. 4: Temperature regulator based on the adsorption principle . . . 10

Fig. 5: Steam pressure curves of hydrocarbons . . . . . . . . . . . 11

Fig. 6: Unit step response of a bulb sensor and a four-bulb sensor . . . 13

Fig. 7: Set point adjustment at temperature sensor . . . . . . . . . . 15

Fig. 8: Excess temperature protection of the sensor . . . . . . . . . . 16

Fig. 9: Sensor locations . . . . . . . . . . . . . . . . . . . . . . 17

Fig. 10: Unit step responses of sensors . . . . . . . . . . . . . . . . 18

Fig. 11: Force balance after increase in temperature. . . . . . . . . . 21

Fig. 12: Reversing device for globe valves in cooling service . . . . . . 22

Fig. 13: Temperature regulator with pressure balanced plug . . . . . . 23

Fig. 14: Three-way mixing valve . . . . . . . . . . . . . . . . . . . 24

Fig. 15: Three-way diverting valve . . . . . . . . . . . . . . . . . . 25

Fig. 16: Example of a heating system . . . . . . . . . . . . . . . . . 26

Fig. 17: Example of a cooling system . . . . . . . . . . . . . . . . . 27

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SAMSON right on quality course

ISO 9001Our quality assurance system,

approved by BVQi, guarantees a high

quality of products and services.

SAMSON AG ⋅ MESS- UND REGELTECHNIK ⋅ Weismüllerstraße 3 ⋅ D-60314 Frankfurt am MainTelefon (069) 4 00 90 ⋅ Telefax (069) 4 00 95 07 ⋅ Internet: http://www.samson.de

2000

/09

⋅L20

5EN

Documents

l205en(Temperature Regulators)