Selection of Kofloc valves

1

Needle valves are divided into two main types: the simplified type and the precision type.

The simplified type has a needle valve knob made integral, and the needle rotates to control flow.

Meanwhile, the precision type has a needle and knob made separately, and the needle moves directly without rotation. The precision type excels in both ease of flow setting and stability. Select an appropriate type in terms of price and accuracy according to the intended usage.

2

The Model 2203 (flow controller) is a constant flow valve that maintains a constant flow when the secondary pressure changes.

Model 2204 (flow controller) maintains a constant flow at the outlet side when the primary flow changes.

The Model 2412 precision needle valve is used for very small flow, while the Model 2412D is used for a wide range of uses as a largecapacity type.

The Models 2400 and 2400D are simplified versions of the Models 2412 and 2412D.

The bellows seal Model 2450 is a low leakage valve that is suitable for use in a vacuum line. The Model 2412M is a precision needle valve equipped with a dial gauge.

3

KOFLOC selects an optimum needle according to the operating
conditions.

4

Advise us of the above, and we can offer the best type irrespective of the needle number.

Of course, we can also manufacture a needle valve according to the specified needle number

Flow characteristics of needle valve

1

The needle used for respective valves comes in various types ac-cording to the flow.

2

The graph shown below summarizes the flow characteristics of representative KOFLOC needle valves.

There may be a slight difference when respective needle valves are actually used because of operating condition errors and instrument errors, as well as the characteristic
summarization based on differential pressure.

In the case of a gas, air is used as a representative for summarization; in the case of other gases, multiply the flow rate by

3

In the case of a liquid, water is used as a representative; in the case
of other liquids, multiply the flow rate by

4

When the viscosity is high, however, contact us for the specific coef-ficient of viscosity.

CAUTION -Precautions on use of needle valves-

Needle valves do not guarantee constant flow continuously.

Opening/closing of other valves, temperature changes, and impact will cause the flow rate to change.

Please determine the period to monitor and readjust the flow rate.

Flow control characteristic CV value

1

The fl w control characteristics of the KOFLOC flow control valves are all represented by the flow characteristics graph shown in GRAPH1.

In the characteristics table (B), the flow changes substantially when the valve is turned slightly, which makes setting difficult and usage unstable.

Therefore, it is necessary to select ser-vice conditions as close to the status (A) as possible.

２.

KOFLOC manufactures valves individually to ensure they match the service conditions.

Simply select the type of valve and specify the supply pressure (primary pressure), outlet pressure (load pressure:
secondary pressure), and maximum operating flow rate, and then we will manufacture a flow control valve with the best control characteristics.

Even if there is no table or graph like the ones shown here, we can select the best valve.

The CV value used as the flow characteristics of needle valves and the like is explained below.

The CV value is a kind of flow coefficient, indicating the approximate flow through a valve when a certain pressure is applied.

P1: Primary-side absolute pressure [MPa·abs]
P2: Secondary-side absolute pressure [MPa·abs]
Q: Flow rate [m3/h]
ρ: Specific gravity (Gas: Air = 1, Liquid: Water = 1)

3

The CV value of a needle valve changes as shown in the GRAPH2 when the valve opening changes. Setting aside the control characteristics, the problem is the flow rate, not selection of an actual valve.

Therefore, the importance point is the maximum CV value shown in the GRAPH2.

4

This text shows the maximum CV values of all needle valves.

When the maximum CV value is substituted in the aforementioned equation to find Q, the maximum flow rate under the operating pressure and temperature conditions is derived.

However, application of this method becomes more difficult as the flow becomes more precise, so use it just as a rough standard.


Suppose 0.075 is the CV value, for example. Let's find the flow rate when the primary pressure (gauge pressure) is 0.1 MPa and the secondary pressure in the atmosphere (gauge pressure) is 0 MPa in cases where air of 20°C is to be controlled. In terms of absolute pressure, the gauge pressure will be 0.1 MPa · abs.

5

Therefore, the flow of 30 l/min can be controlled when the valve
operates between the fully-open and fully-closed states under the
above conditions.

Principle of Flow Control Valve

(1) Flow control with needle valve

The needle valve controls the opening of a small orifice in a channel with a bar-shaped needle, controlling the flow by changing the channel resistance. The valve thus acts as a resistance.

The flow changes when the pressure applied to the valve changes. Therefore, a pressure regulator is provided in the preceding stage as shown in Fig. A to make the pressure applied to the valve constant, thereby
obtaining constant flow. This is an inexpensive method which is commonly used when the pressure loss on the valve outlet side does not change. Use a simplified type, precision type, or bellows type needle valve according to the usage.

(2) Flow control with variable primary pressure type flow controller

The variable primary pressure (supply pressure) type flow controller is made by combining the needle valve (1) and a pressure regulator.

It can keep the flow constant even if the primary-side pressure changes.
(Fig. B).

(3) Flow control with variable secondary pressure type flow controller

In methods (1) and (2), the flow will change if the pressure loss of a load in the subsequent stage is large.

In that case, a variable secondary pressure (outlet-side pressure: load pressure) type flow controller is used to control flow according to the flow sheet shown in Fig. C.

This flow sheet is complete with respect to pressure change, and is used basically for our gas mixing equipment. The primary-side pressure is controlled by a regulator, and the flow controller immune to pressure changes on the secondary side enables flow control free of the influence of the primary and secondary pressure.

Proximity sensor type and working principle

Inductive & CapacitiveTheir operating principle is based on a high frequency oscillator that creates a field in the close surroundings of the sensing surface. The presence of a metallic object (inductive) or any material (capacitive) in the operating area causes a change of the oscillation amplitude. The rise or fall of such oscillation is identified by a threshold circuit that changes the output state of the sensor. The operating distance of the sensor depends on the actuator's shape and size and is strictly linked to the nature of the material (Table 1 & Table 2.). A screw placed on the back of the capacitive sensor allows regulation of the operating distance. This sensitivity regulation is useful in applications, such as detection of full containers and non-detection of empty containers.
Table 1: INDUCTIVE SENSORS Sensitivity when different metals are present. Sn = operating distance. Fe37 (iron) Stainless steel Brass- bronze Aluminum Copper 1 x Sn 0.9 x Sn 0.5 x Sn 0.4 x Sn 0.4 x Sn	Table 2: CAPACITIVE SENSORS Sensitivity when different materials are present. Sn = operating distance. Metal Water Plastic Glass Wood 1 x Sn 1 x Sn 0.5 x Sn 0.5 x Sn 0.4 x Sn
Photoelectric These sensors use light sensitive elements to detect objects and are made up of an emitter (light source) and a receiver. Three types of photoelectric sensors are available. Direct Reflection - emitter and receiver are housed together and uses the light reflected directly off the object for detection. Reflection with Reflector - emitter and receiver are housed together and requires a reflector. An object is detected when it interrupts the light beam between the sensor and reflector. Thru Beam - emitter and receiver are housed separately and detects an object when it interrupts the light beam between the emitter and receiver. Magnetic Magnetic sensors are actuated by the presence of a permanent magnet. Their operating principle is based on the use of reed contacts, which consist of two low reluctance ferro-magnetic reeds enclosed in glass bulbs containing inert gas. The reciprocal attraction of both reeds in the presence of a magnetic field, due to magnetic induction, establishes an electrical contact.

Pressure transmitter working principle and type

A pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical.
Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators and piezometers, manometers, among other names.
Pressure sensors can vary drastically in technology, design, performance, application suitability and cost. A conservative estimate would be that there may be over 50 technologies and at least 300 companies making pressure sensors worldwide.
There is also a category of pressure sensors that are designed to measure in a dynamic mode for capturing very high speed changes in pressure. Example applications for this type of sensor would be in the measuring of combustion pressure in an engine cylinder or in a gas turbine. These sensors are commonly manufactured out of piezoelectric materials such as quartz.
Some pressure sensors, such as those found in some traffic enforcement cameras, function in a binary (on/off) manner, i.e., when pressure is applied to a pressure sensor, the sensor acts to complete or break an electrical circuit. These types of sensors are also known as a pressure switch.

Types of pressure measurements

silicon piezoresistive pressure sensors

Pressure sensors can be classified in terms of pressure ranges they measure, temperature ranges of operation, and most importantly the type of pressure they measure. In terms of pressure type, pressure sensors can be divided into five categories:

• Absolute pressure sensor

This sensor measures the pressure relative to perfect vacuum pressure (0 PSI or no pressure). Atmospheric pressure, is 101.325 kPa (14.7 PSI) at sea level with reference to vacuum.

• Gauge pressure sensor

This sensor is used in different applications because it can be calibrated to measure the pressure relative to a given atmospheric pressure at a given location. A tire pressure gauge is an example of gauge pressure indication. When the tire pressure gauge reads 0 PSI, there is really 14.7 PSI (atmospheric pressure) in the tire.

• Vacuum pressure sensor

This sensor is used to measure pressure less than the atmospheric pressure at a given location. This has the potential to cause some confusion as industry may refer to a vacuum sensor as one which is referenced to either atmospheric pressure (i.e. measure Negative gauge pressure) or relative to absolute vacuum.

• Differential pressure sensor

This sensor measures the difference between two or more pressures introduced as inputs to the sensing unit, for example, measuring the pressure drop across an oil filter. Differential pressure is also used to measure flow or level in pressurized vessels.

• Sealed pressure sensor

This sensor is the same as the gauge pressure sensor except that it is previously calibrated by manufacturers to measure pressure relative to sea level pressure.

Pressure-sensing technology

There are two basic categories of analog pressure sensors.
Force collector types These types of electronic pressure sensors generally use a force collector (such a diaphragm, piston, bourdon tube, or bellows) to measure strain (or deflection) due to applied force (pressure) over an area.

• Piezoresistive strain gauge

Uses the piezoresistive effect of bonded or formed strain gauges to detect strain due to applied pressure. Common technology types are Silicon (Monocrystalline), Polysilicon Thin Film, Bonded Metal Foil, Thick Film, and Sputtered Thin Film. Generally, the strain gauges are connected to form a Wheatstone bridge circuit to maximize the output of the sensor. This is the most commonly employed sensing technology for general purpose pressure measurement. Generally, these technologies are suited to measure absolute, gauge, vacuum, and differential pressures.

• Capacitive

Uses a diaphragm and pressure cavity to create a variable capacitor to detect strain due to applied pressure. Common technologies use metal, ceramic, and silicon diaphragms. Generally, these technologies are most applied to low pressures (Absolute, Differential and Gauge)

• Electromagnetic

Measures the displacement of a diaphragm by means of changes in inductance (reluctance), LVDT, Hall Effect, or by eddy current principle.

• Piezoelectric

Uses the piezoelectric effect in certain materials such as quartz to measure the strain upon the sensing mechanism due to pressure. This technology is commonly employed for the measurement of highly dynamic pressures.

• Optical

Uses the physical change of an optical fiber to detect strain due to applied pressure. A common example of this type utilizes Fiber Bragg Gratings. This technology is employed in challenging applications where the measurement may be highly remote, under high temperature, or may benefit from technologies inherently immune to electromagnetic interference.

• Potentiometric

Uses the motion of a wiper along a resistive mechanism to detect the strain caused by applied pressure.

Other types
These types of electronic pressure sensors use other properties (such as density) to infer pressure of a gas, or liquid.

• Resonant

Uses the changes in resonant frequency in a sensing mechanism to measure stress, or changes in gas density, caused by applied pressure. This technology may be used in conjunction with a force collector, such as those in the category above. Alternatively, resonant technology may be employed by expose the resonating element itself to the media, whereby the resonant frequency is dependent upon the density of the media. Sensors have been made out of vibrating wire, vibrating cylinders, quartz, and silicon MEMS. Generally, this technology is considered to provide very stable readings over time.

• Thermal

Uses the changes in thermal conductivity of a gas due to density changes to measure pressure. A common example of this type is the Pirani gauge.

• Ionization

Measures the flow of charged gas particles (ions) which varies due to density changes to measure pressure. Common examples are the Hot and Cold Cathode gages.

• Others

There are numerous other ways to derive pressure from its density (speed of sound, mass, index of refraction) among others.

Applications

There are many applications for pressure sensors:

• Pressure sensing

This is the direct use of pressure sensors to measure pressure. This is useful in weather instrumentation, aircraft, cars, and any other machinery that has pressure functionality implemented.

• Altitude sensing

This is useful in aircraft, rockets, satellites, weather balloons, and many other applications. All these applications make use of the relationship between changes in pressure relative to the altitude. This relationship is governed by the following equation^[1]:

This equation is calibrated for an altimeter, up to 36,090 feet (11,000 m). Outside that range, an error will be introduced which can be calculated differently for each different pressure sensor. These error calculations will factor in the error introduced by the change in temperature as we go up.
Barometric pressure sensors can have an altitude resolution of less than 1 meter, which is significantly better than GPS systems (about 20 meters altitude resolution). In navigation applications altimeters are used to distinguish between stacked road levels for car navigation and floor levels in buildings for pedestrian navigation.

• Flow sensing

This is the use of pressure sensors in conjunction with the venturi effect to measure flow. Differential pressure is measured between two segments of a venturi tube that have a different aperture. The pressure difference between the two segments is directly proportional to the flow rate through the venturi tube. A low pressure sensor is almost always required as the pressure difference is relatively small.

• Level / depth sensing

A pressure sensor may also be used to calculate the level of a fluid. This technique is commonly employed to measure the depth of a submerged body (such as a diver or submarine), or level of contents in a tank (such as in a water tower). For most practical purposes, fluid level is directly proportional to pressure. In the case of fresh water where the contents are under atmospheric pressure, 1psi = 27.7 inH20 / 1Pa = 9.81 mmH20. The basic equation for such a measurement is

where P = pressure, p = density of the fluid, g = standard gravity, h = height of fluid column above pressure sensor

• Leak testing

A pressure sensor may be used to sense the decay of pressure due to a system leak. This is commonly done by either comparison to a known leak using differential pressure, or by means of utilizing the pressure sensor to measure pressure change over time.

Types of Encoder

Absolute rotary encoder

Mechanical absolute encoders
A metal disc containing a set of concentric rings of openings is fixed to an insulating disc, which is rigidly fixed to the shaft. A row of sliding contacts is fixed to a stationary object so that each contact wipes against the metal disc at a different distance from the shaft. As the disc rotates with the shaft, some of the contacts touch metal, while others fall in the gaps where the metal has been cut out. The metal sheet is connected to a source of electric current, and each contact is connected to a separate electrical sensor. The metal pattern is designed so that each possible position of the axle creates a unique binary code in which some of the contacts

Optical absolute encoders
The optical encoder's disc is made of glass or plastic with transparent and opaque areas. A light source and photo detector array reads the optical pattern that results from the disc's position at any one time.
This code can be read by a controlling device, such as a microprocessor or microcontroller to determine the angle of the shaft.
The absolute analog type produces a unique dual analog code that can be translated into an absolute angle of the shaft (by using a special algorithm).

Standard binary encoding

Rotary encoder for angle-measuring devices marked in 3-bit binary. The inner ring corresponds to Contact 1 in the table. Black sectors are "on". Zero degrees is on the right-hand side, with angle increasing counterclockwise.

An example of a binary code, in an extremely simplified encoder with only three contacts, is shown below.

Standard Binary Encoding

Sector	Contact 1	Contact 2	Contact 3	Angle
1	off	off	off	0° to 45°
2	off	off	ON	45° to 90°
3	off	ON	off	90° to 135°
4	off	ON	ON	135° to 180°
5	ON	off	off	180° to 225°
6	ON	off	ON	225° to 270°
7	ON	ON	off	270° to 315°
8	ON	ON	ON	315° to 360°

In general, where there are n contacts, the number of distinct positions of the shaft is 2ⁿ. In this example, n is 3, so there are 2³ or 8 positions.
In the above example, the contacts produce a standard binary count as the disc rotates. However, this has the drawback that if the disc stops between two adjacent sectors, or the contacts are not perfectly aligned, it can be impossible to determine the angle of the shaft. To illustrate this problem, consider what happens when the shaft angle changes from 179.9° to 180.1° (from sector 4 to sector 5). At some instant, according to the above table, the contact pattern changes from off-on-on to on-off-off. However, this is not what happens in reality. In a practical device, the contacts are never perfectly aligned, so each switches at a different moment. If contact 1 switches first, followed by contact 3 and then contact 2, for example, the actual sequence of codes is:

off-on-on (starting position)

on-on-on (first, contact 1 switches on)

on-on-off (next, contact 3 switches off)

on-off-off (finally, contact 2 switches off)

Now look at the sectors corresponding to these codes in the table. In order, they are 4, 8, 7 and then 5. So, from the sequence of codes produced, the shaft appears to have jumped from sector 4 to sector 8, then gone backwards to sector 7, then backwards again to sector 5, which is where we expected to find it. In many situations, this behaviour is undesirable and could cause the system to fail. For example, if the encoder were used in a robot arm, the controller would think that the arm was in the wrong position, and try to correct the error by turning it through 180°, perhaps causing damage to the arm.


Gray encoding

Rotary encoder for angle-measuring devices marked in 3-bit binary-reflected Gray code (BRGC). The inner ring corresponds to Contact 1 in the table. Black sectors are "on". Zero degrees is on the right-hand side, with angle increasing anticlockwise.

To avoid the above problem, Gray encoding is used. This is a system of binary counting in which adjacent codes differ in only one position. For the three-contact example given above, the Gray-coded version would be as follows.

Gray Coding

Sector	Contact 1	Contact 2	Contact 3	Angle
1	off	off	off	0° to 45°
2	off	off	ON	45° to 90°
3	off	ON	ON	90° to 135°
4	off	ON	off	135° to 180°
5	ON	ON	off	180° to 225°
6	ON	ON	ON	225° to 270°
7	ON	off	ON	270° to 315°
8	ON	off	off	315° to 360°

In this example, the transition from sector 4 to sector 5, like all other transitions, involves only one of the contacts changing its state from on to off or vice versa. This means that the sequence of incorrect codes shown in the previous illustration cannot happen.


Single-track Gray encoding
If the designer moves a contact to a different angular position (but at the same distance from the center shaft), then the corresponding "ring pattern" needs to be rotated the same angle to give the same output. If the most significant bit (the inner ring in Figure 1) is rotated enough, it exactly matches the next ring out. Since both rings are then identical, the inner ring can be omitted, and the sensor for that ring moved to the remaining, identical ring (but offset at that angle from the other sensor on that ring). Those two sensors on a single ring make a quadrature encoder.
For many years, Torsten Sillke and other mathematicians believed that it was impossible to encode position on a single track so that consecutive positions differed at only a single sensor, except for the two-sensor, one-track quadrature encoder. However, in 1994 N. B. Spedding registered a patent (NZ Patent 264738) showing it was possible with several examples. See Single-track Gray code for details