Device tolerances

Similar exercises must be performed to identify synthetic nanocomponents. Considerations include suitability for the proposed environment, synthesis and handling properties, polydispersity, structural / chemical properties, as well as amenability to assembly into higher order structures. For medical devices, tolerability and safety of the structural materials is also an issue. Current materials technology offers powerful, but limited capacity to engineer an off the shelf approach to nanostructures. 

The Performance Analysis capabilities of Probe are used to view properties of waveforms that are not easily described. Examples are amplifier bandwidth, rise time, and overshoot. To calculate the bandwidth of a circuit, you must find the maximum gain, and then find the frequency where the gain is down by 3 dB. To calculate rise time, you must find the 10% and 90% points, and then find the time difference between the points. The Performance Analysis gives us the capability to plot these properties versus a parameter or device tolerances. Hie Performance Analysis is used in conjunction with the Parametric Sweep to see how the properties vary versus a parameter. The Performance Analysis is used in conjunction with the Monte Carlo analysis to see how the properties vary with device tolerances. In this section we will plot the bandwidth of an amplifier versus the value of the feedback resistor. See Sections 9.B.3 and 9.E to see how to use the Performance Analysis in conjunction with the Monte Carlo analysis. 

The Monte Carlo analyses are used to observe how device tolerances can affect a design. There are two analyses that can be performed. The Worst Case analysis is used to find the maximum or minimum value of a parameter given device tolerances. Device tolerances are varied to their maximum or minimum limits such that the maximum or minimum of the specified parameter is found. The Monte Carlo analysis is used to find production yield. If the Worst Case analysis shows that not all designs will pass a specific criterion, the Monte Carlo analysis can be used to estimate what percentage will pass. The Monte Carlo analysis varies device parameters within the specified tolerance. The analysis randomly picks a value for each device that has tolerance and simulates the circuit using the random values. A specified output can be observed. 

This part discusses the syntax of models with device tolerance and how to use the models in a simulation. This part does not discuss how to easily create models within Capture. After you have understood the syntax for the models and how to run the simulations, you may wish to look at Part 7 to see how to create new models to specify the tolerance you need. 

The Performance Analysis can be used in conjunction with the Monte Carlo analysis to view the distribution of a parameter as a function of device tolerances. For this example, we will display how the spread of the gain V(Vo)/V(Vl) varies with resistor tolerances. We will use the voltage divider of the previous section and 5% resistors with a uniform distribution ... 

In amplifier design it is important to know how your bias will change with device tolerances. In this section we will find the minimum and maximum collector current of a BJT when we include variations in the transistor current gain, 0F, and resistor tolerances. The circuit above was previously simulated in the Transient Analysis and AC Sweep parts. We will use the same resistor values as before, but we will change the resistor models to include tolerance. The BJT is also changed to the model QBf. This model allows 0F to have a uniform distribution between 50 and 350. 

When designing digital circuits we are usually concerned with the rise and fall times of the design, given device tolerances. The example given here is for a CMOS inverter, but the procedure used can be applied to any switching circuit with device tolerances. Wire the circuit below ... 

We would like to see how the rise and fall times vary with random device tolerances. We must set up the Transient Analysis to view waveforms versus time, and the Monte Carlo analysis to allow for device variations. First we will look at the input pulsed waveform. The property spreadsheet for Vi is ... 

This is our input trace. We see that it has no variation with device tolerances, as should be expected. Delete the trace Vflfln) and then add the trace V(VO) ... 

A tubular sonicatlon device was recently reported by Borthwick et al. [93] (see Fig. 3.9). The device requires the addition of no chemical, enzyme or particles that might complicate the subsequent determination step. Furthermore, denaturatlon of target DMA or proteins for detection Is minimized as the device tolerates moderate temperature rises this allows the use of sensitive and specific Immunological detection methods on sonicated biological materials. Because the tubular device Is composed of a piezoelectric resonator made of several material layers, selection of an appropriate operating frequency Is essential to ensure proper performance (i.e. acceptable cell disruption efficiency). This device can be used for batchwise treatment of small sample volumes or In flow systems without the risk of hazardous aerosol formation inherent in probe sonloators. 

Use resilient aduator or operate within device tolerance. 

Handbook 44, Specifications, Tolerances, and Other Technical Requirements Tor Weighing and Measuring Devices, National Institute of Standards and Technology, Gaithersburg, Md., 1996. 

A constant temperature is required for close-tolerance measuring, gauging, machining, or grinding operations, to prevent expansion and contraction of machine parts, machined products, and measuring devices. In this instance a constant temperature is normally more important than the temperature level. Relative humidity is secondary in importance but should not go above 45% to minimise formation of a surface moisture film. 

At locations where variable support reactions are not tolerable over the required movement range, constant-effort springs or counterweights ate used. Piping systems supported entirely by constant-effort devices requite precise accuracy to counterbalance the total piping load, otherwise the system may be vertically unstable. 

Dry-heat sterilization is generally conducted at 160—170°C for >2 h. Specific exposures are dictated by the bioburden concentration and the temperature tolerance of the products under sterilization. At considerably higher temperatures, the required exposure times are much shorter. The effectiveness of any cycle type must be tested. For dry-heat sterilization, forced-air-type ovens are usually specified for better temperature distribution. Temperature-recording devices are recommended. 

Pressure-relief-device requirements are defined in Subsec. A. Set point and maximum pressure during relief are defined according to the service, the cause of overpressure, and the number of relief devices. Safety, safety relief, relief valves, rupture disk, breaking pin, and rules on tolerances for the reheving point are given. 

Cleanable Granular-Bed Filters The principal objective in the development of cleanable granular-bed filters is to produce a device that can operate at temperatures above the range that can be tolerated with fabric filters. In some of the devices, the granules are circulated continuously through the unit, then are cleaned of the collected dust and returned to the filter bed. In others, the granular bed remains in place but is periodically taken out of service and cleaned by some means, such as backflushing with air. 

The factors discussed in Section 23.5.2 give rise directly to the current drawn by the capacitor unit and indirectly add to its rating. The relevant Standards on this device recommend a continuous overload capacity of 30% to account for all such factors. A capacitor can have a tolerance of up to -t-15% in its capacitance value (Section 26.3.1(1)). All current-carrying components such as breakers, contactors, switches, fuses, cables and busbar systems associated with a capacitor unit or its banks, must therefore be rated for at least 1.3 x 1.15/,., i.e. 1.54. For circuits where higher amplitudes of harmonics are envisaged, for reasons of frequent load variations or more... 

Ductility. A load-bearing device or component must not distort so much under the action of the service stresses that its function is impaired, nor must it fail by rupture, though local yielding may be tolerable. Therefore, high modulus and high strength, with ductility, is the desired combination of attributes. However, the inherent nature of plastics is such that high modulus tends to be associated with low ductility and steps that are taken to improve the one cause the other to deteriorate. The major effects are summarised in Table 1.6. Thus it may be seen that there is an almost inescapable rule by which increased modulus is accompanied by decreased ductility and vice versa. 

Constriction measurement devices constructed to standards do not necessarily require calibration. One idea of strict standardization is to define the manufacturing, tolerances, and other features in such a way that the instruments made according to these rules require no calibration. The properties are so well known that a certain accuracy can be guaranteed. If the accuracy specified in the standard is inadequate, additional calibration procedures are required. The same applies to Pitot-static tubes made according to standard specifications." ... 

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