Foot Step Bearing Engineering Drawing

Mass, force, and torque measurement

Alan S. Morris , Reza Langari , in Measurement and Instrumentation (Third Edition), 2021

Beam balance

The beam balance is used for calibrating masses in the range between 10  mg and 1   Kg. The measurement resolution and accuracy achieved depends on the quality and sharpness of the knife edge that the pivot is formed from. For high measurement resolution, friction at the pivot must be as close to zero as possible, and hence a very sharp and clean knife-edge pivot is demanded. The two halves of the beam on either side of the pivot are normally of equal length and are measured from the knife edge. Any bluntness, dirt, or corrosion in the pivot can cause these two lengths to become unequal, causing consequent measurement errors. Similar comments apply about the knife edges on the beam that the two pans are hung from. It is also important that all knife edges are parallel, otherwise displacement of the point of application of the force over the line of the knife edge can cause further measurement errors. This last form of error also occurs if the mass is not placed centrally on the pan.

Great care is therefore required in the use of such an instrument, and, provided that it is kept in good condition, particularly with regard to keeping the knife edges sharp and clean, high measurement accuracy is achievable. Such good condition can be confirmed by applying calibrated masses to each side of the balance. If the instrument is then exactly balanced, all is well.

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Suspension

Heinz Heisler MSc., BSc., F.I.M.I., M.S.O.E., M.I.R.T.E., M.C.I.T., M.I.L.T. , in Advanced Vehicle Technology (Second Edition), 2002

10.13.1 Equalization of vehicle laden weight between axles (Figs 10.88 and 10.89)

Consider a reactive balance beam tandem axle bogie rolling over a hump or dip in the road (Fig. 10.88). The balance beam will tilt so that the rear end of the first axle is lifted upwards and the front end of the second axle will be forced downward. Consequently both pairs of axle wheels will be compelled to contact the ground and equally share out the static laden weight imposed on the whole axle bogie.

Fig. 10.88. Payload distribution with reactive balance beam and swing shackles

The tilting of the balance beam will lift the first axle a vertical distance h/2, which is half the hump or dip's vertical height. The second axle will fall a similar distance h/2. The net result is that the chassis with the tandem axle bogie will only alter its height relative to ground by half the amount of a single axle suspension layout (Fig. 10.88). Thus the single axle suspension will lift or lower the chassis the same amount as the axle is raised or lowered from some level datum, whereas the tandem axle bogie only changes the chassis height relative to the ground by half the hump lift or dip drop.

In contrast to the halving of the vertical lift or fall movement of the chassis with tandem axles, there are two vertical movements with a tandem axle as opposed to one for a single axle each time the vehicle travels over a bump. Thus the frequency of the chassis vertical lift or fall with tandem axles will be twice that for a single axle arrangement.

Similar results will be achieved if a central pivoting inverted transverse spring tandem axle bogie rides over a hump or dip in the road (Fig. 10.89). Initially the first axle will be raised the same distances as the hump height h, but the central pivot will only lift half the amount h/2. Conversely if the first axle goes into a dip, the second axle will be above the first axle by the height of the dip, but the chassis will only be lowered by half this vertical movement h/2. Again the frequency of lift and fall of the chassis as the tandem axles move over the irregularities in the road will be double the frequency compared to a single axle suspension.

Fig. 10.89. Payload distribution with single inverted semi-elliptic spring

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Movable bridges

R. Saul , K. Humpf , in Innovative Bridge Design Handbook, 2016

5.1 Design concept

This section discusses the design for a DBBB proposed by Saul and Humpf (2007). So far, balance beam bridges have been built as single-span bridges. Due to the articulation of the balance beam, this system takes permanent loads only. In DBBBs, the joint at the center would have to transmit under live loads the bending moment of a single-span beam. If, instead, the rotation of the balance beam is blocked by a second bearing, the staying system also participates in handling the live loads. This allows balance beam bridges to be built with two flaps, thereby doubling their span range. This solution is advantageous in areas where the piers of a bascule bridge have to be built in water or groundwater.

In more detail, we make use of the fact that for cinematic reasons, the balance beam has to have an eccentricity toward land. With an additional bearing with eccentricity toward the water – which can take compression only and is automatically activated when lowering the flaps (Figure 17.32) – the live loads can also be taken by the balance beam and the pylon, and thereby, the moments of the bridge deck – especially at the center – are substantially reduced.

Figure 17.32. Bearing at the top of the tower of a DBBB.

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Air operated power brake equipment and vehicle retarders

Heinz Heisler MSc., BSc., F.I.M.I., M.S.O.E., M.I.R.T.E., M.C.I.T., M.I.L.T. , in Advanced Vehicle Technology (Second Edition), 2002

12.3.11 Dual delta series foot control valve (Fig. 12.16)

Purpose The delta series of dual foot valves provide the braking system with two entirely separate foot controlled air valve circuits but which operate simultaneously with each other. Thus, if one half of the dual foot valve unit should develop a fault then the balance beam movement will automatically ensure that the other half of the twin valve unit continues to function.

Operation

Brakes released (12.16(a)) When the brakes are released, the return springs push up the piston, graduating spring and plunger assemblies for each half valve unit. Consequently the inlet disc valves close and the control tube shaped exhaust valves open. This permits air to exhaust through the centre of the piston tube, upper piston chamber and out to the atmosphere.

Fig. 12.16 (a and b). Dual delta foot control valve

Brakes applied (12.16(b)) When the foot treadle is depressed, a force is applied centrally to the balance beam which then shares the load between both plunger spring and piston assemblies. The downward plunger load initially pushes the piston tubular stem on its seat, closing the exhaust disc valve, and with further downward movement unseats and opens the inlet disc valve. Air from the reservoirs will now enter the lower piston chambers on its way to the brake actuators via the delivery ports.

As the air pressure builds up in the lower piston chambers it will oppose and compress the graduating springs until it eventually closes the inlet valve. The valve assembly is then in a lapped or balanced position where both exhaust and inlet valves are closed. Only when the driver applies an additional effort to the treadle will the inlet valve again open to allow a corresponding increase in pressure to pass through to the brake actuator.

The amount the inlet valve opens will be proportional to the graduating spring load, and the pressure reaching the brake actuator will likewise depend upon the effective opening area of the inlet valve. Immediately the braking effort to the foot treadle is charged, a new state of valve lap will exist so that the braking power caused by the air operating on the wheel brake actuator will be progressive and can be sensed by the driver by the amount of force being applied to the treadle. When the driver reduces the foot treadle load, the inlet valve closes and to some extent the exhaust valve will open, permitting some air to escape from the actuator to the atmosphere via central tube passages in the dual piston tubes. Thus the graduating spring driver-controlled downthrust and the reaction piston air-controlled upthrust will create a new state of valve lap and a corresponding charge to the braking power.

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Introduction to the Effect of Heat Aging on Plastics

Laurence W. McKeen , in The Effect of Long Term Thermal Exposure on Plastics and Elastomers, 2014

2.4.2.1 Thermogravimetric Analysis

TGA is the most widely used thermal method. It is based on the measurement of mass loss of material as a function of temperature. The instrument used in thermogravimetry (TG) is called a thermobalance. Typically the thermobalance measures and records the change in weight of the test material as the temperature is slowly ramped up. It produces a TG curve such as that shown in Figure 2.19.

Figure 2.19. Example of TG curve of and epoxy–glass resin.

Basic components of a typical thermobalance, a picture of which is shown in Figure 2.20 are the following:

Figure 2.20. Picture of a typical thermogravimetric analyzer.

1.

The balance is highly sensitive and accurate having a measuring range from 0.0001   mg to 1   g. Recording balances are of two types, null point and deflection type. The null type balance, which is more widely used, incorporates a sensing element which detects a deviation of the balance beam from its null position, A sensor detects the deviation and triggers the restoring force to bring the balance beam back to the null position. The restoring force is directly proportional to the mass change. Deflection balance of the beam type involves the conversion of the balance beam deflection about the fulcrum into a suitable mass.

2.

Furnace : Generally has a wide temperature range −150°C to 2000°C and must be designed to produce linear heating over this range. The linear heating is controlled at selectable rates.

3.

Unit for temperature measurement and control (Programmer).

4.

Recorder: Automatic recording unit for the mass and temperature changes.

5.

Provisions are made to purge the furnace with an inert gas or with air or oxygen.

6.

Some units will collect the volatiles for chemical analysis by mass spectroscopy or infrared spectroscopy.

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Final Control Element

Swapan Basu , Ajay Kumar Debnath , in Power Plant Instrumentation and Control Handbook (Second Edition), 2019

5.1.3 E(I)/P Converter (Fig. 6.34A and B)

This converts the electrical control signal in to a pneumatic one. In the case of an intelligent positioner, this forms part of the positioner. Out of various types of E(I)/P converters available in the market, one that works on a force balance principle is the simplest and most popular. Mounting details and working principles have been shown in Fig. 6.34A and B. There is a plunger coil near a permanent magnet, with two poles on the opposite side of the fulcrum. When the system is in a balanced condition, the balance beam is in equilibrium to give a pneumatic output proportional to current into the device. When the current input to the plunger coil increases, the coil on the right side of the plunger is pulled towards the right side, so the flapper is pushed towards the nozzle. As a result, there will be an increase in back pressure and pressure in the diaphragm, which will try to close the exhaust, and the output air pressure of the E/P converter increases. This also causes an increase in feedback below to bring the balance beam to its equilibrium position once the forces are balanced. There will be zero adjustment to the bellow or the span adjusting spring. There could be other possibilities where the plunger coil force is balanced by the dynamic back pressure as shown in Fig. 6.34B (in the upper part of the drawing, based on SAMSON document) (Table 6.23).

Table 6.23. E(I)/P Converter (DS)

Sl	Specifying Point	Standard/Available Data	To Be Specified
1	Input	0/4–20   mA DC (for split operation 4–12 or 12–20   mA DC may be available (e.g., Model no. TEIP of ABB)	To specify
2	Output	0.2–1.0 kg/cm2 or 3–15 psi, or 0.2–1.0 bar intermediate/higher ranges like 6–30 psi, etc. are also possible (e.g., Model no. TEIP of ABB)	To specify
3	Ex proof approval	Possible if applicable to indicate the desired certification standard	To specify
4	Characteristics	Linear—direct/reverse
5	Air supply/capacity/consumption	1.4–5.4 bar (Supply pressure)/~2.0–8 Nm3/h (Capacity)/0.16 Nm3/h (Consumption)	All figures mentioned here are typical only
6	Encl. class	IP 65/NEMA 4	To specify
7	Hysteresis/sensitivity	0.3%/0.1% of FSD
8	Accuracy	<   0.5% FSD
9	Influence variables	Air supply/vibration/mounting position	Manufacturer std.
10	Connection	6   mm/¼″ NPT, etc.
11	Materials of construction	Die cast aluminum/plastic manufacturer Std.
12	Accessories	Mounting bracket for 2″ pipe mounting/wall mounting
13	Environmental	(−)20–80°C 97% humidity
14	Special feature	Construction ruggedness, vibration effect, lightweight, and dynamic response	Split range if desired (to specify)

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Final Control Element

Swapan Basu , Ajay Kumar Debnath , in Power Plant Instrumentation and Control Handbook, 2015

5.3 E(I)/P Converter

The E(I)/P converter converts the electrical control signal into a pneumatic one. In an intelligent positioner, this forms part of the positioner. Of the various types of E(I)/P converters available commercially, the simplest and most popular is the one that works on the force balance principle. For mounting details and working principles, see Figure VI/5.3-1a and b. There is a plunger coil near a permanent magnet, with two poles on the opposite side of the fulcrum. When the system is in a balanced condition the balance beam is in equilibrium to produce a pneumatic output proportional to the current in to the device. When the current input to the plunger coil increases, the right side coil of the plunger is pulled toward the right side, so the flapper is pushed toward the nozzle. As a result, there will be increased back pressure and pressure in the diaphragm, which will try to close the exhaust, and the output air pressure of the E/P converter increases. This also causes increased feedback below to bring the balance beam to its equilibrium position, as soon as the forces are balanced. There is a zero adjusting bellow and span-adjusting spring. There could be other possibilities where plunger coil force is balanced by the dynamic back pressure as shown in Figure VI/5.3-1b (in the upper part of the drawing; based on a SAMSON document). There is an E(I)/P converter data sheet in Table VI/5.3.1-1.

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Bridge circuits

Jim Williams , in Analog Circuit Design, 2011

Publisher Summary

Bridge circuits are among the most elemental and powerful electrical tools. They are found in measurement, switching, oscillator, and transducer circuits. Additionally, bridge techniques are broadband, serving from DC to bandwidths well into the GHz range. Being the electrical analog of the mechanical beam balance, they are also the progenitor of all electrical differential techniques. An almost uncountable number of tricks and techniques have been applied to enhance linearity, sensitivity, and stability of the basic configuration. In particular, transducer manufacturers are quite adept at adapting the bridge to their needs. Careful matching of the transducer's mechanical characteristics to the bridge's electrical response can provide a trimmed, calibrated output. Similarly, circuit designers have altered performance by adding active elements to the bridge, excitation source, or both. A primary concern is the accurate determination of the differential output voltage. Bridge amplifiers are designed to accurately extract the bridge's differential output from its common mode level. The common mode suppression circuits shown require a negative power supply. Often, such circuits must function in systems where only a positive rail is available. The bridge's inherent nonlinear output is also accommodated by the processor. Level transducers which measure angle from ideal level are employed in road construction, machine tools, inertial navigation systems, and other applications requiring a gravity reference.

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Ultrasonic Cleaning

S.B. Awad , R. Nagarajan , in Developments in Surface Contamination and Cleaning: Particle Deposition, Control and Removal, 2010

4.3 Microbalance

A microbalance may be used to quantify mass loss from a coupon by cavitation erosion. The Cahn C-34/C-35™ microbalance is one such sensitive weight and force measurement instrument. It is designed for weights and forces up to 3.5 g and is sensitive to changes as small as 0.1 μg. The balance may be described as a force-to-current converter. It consists of: (1) a balance beam mounted to, supported by, and pivoting about the center of a taut ribbon; (2) a torque motor coil located in a permanent magnetic field and also mounted to the taut ribbon; (3) sample suspension fixtures; (4) a beam position sensor system; and (5) controls, circuitry, and indicators (Figure 6.25).

FIGURE 6.25. Schematic diagram of the Cahn microbalance.

Weights or forces to be measured are applied to the sample (left) side of the beam, which produces a force about the axis of rotation. An electric current flowing in the torque motor also produces a force about the same axis that is equal and opposite to the force from the beam, if the beam is at the beam reference position. This reference position is detected by the beam position sensing system. A greater force on the beam will require a greater opposite force from the torque motor in order to keep the beam at its reference position. Therefore, the current necessary to produce the required torque motor force is a direct measure of the force on the beam. The process of calibration allows this current to be measured in units of weight (grams).

In order to measure mass loss due to ultrasonic cleaning, the material coupon is first cleaned with pure water and dried in the oven so that it loses all its moisture and is weighed using the microbalance before immersing in a beaker full of water. This beaker is then suspended at the center of the tank using a fixture to hold it. The ultrasonic generator is switched on and the power level is adjusted. Experiments may be done to simulate even mild cavitation conditions (132–192 kHz) and low power inputs. After a certain time (say, 2 minutes) the generator is turned off. The specimen is then taken out and dried in the oven. When the specimen is dry, it is taken out and re-weighed using the microbalance. This step is repeated in a multiple-extraction mode.

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Foot Step Bearing Engineering Drawing

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