Demand rate

A goal of controlled release fertiliser research since the 1940s has been the development of a product that deUvers its nutrients at a rate matching the demand rate of the plant to which it is appHed. Such a fertiliser would represent the ultimate in use efficiency agronomic performance, ie, crop yield, quahty, and appearance agronomic safety and labor savings, ie, reduced appHcation frequency. It also would minimise potential losses to the environment. 

The IEEE Std 500 document is based on a hierarchical structure of component types set down in the manual s table of contents. The preface for each subsection (defined by a component type) provides a tree diagram that clearly shows the way the component classes have been subdivided to determine "data cells". The failure modes for each component class are also hierarchically organized according to failure severity catastrophic, degraded, or incipient. Rates per hour and demand rates (per cycle) are both included, as well as upper and lower bounds. 

There is an alternative to using neat butane vapor, however, which overcomes the need for pipework heating. This is to use a gas-air mixture. A special gas-air mixer is used which ensures that a preset ratio is maintained at all demand rates. The ratio chosen must be well outside the flammable limits. A typical LPG-air-mixing plant is illustrated by Figure 20.7. 

ESD systems should be designed to be sufficiently reliable and fail safe that a (1) accidental initiation of the ESD is reduced to acceptable low levels or as low as reasonably practical, (2) availability is maximized as a function of the frequency of system testing and maintenance, and (3) the fractional MTBF of the system is sufficiently large to reduce the hazard rate to an acceptable level, consistent with the demand rate of the system. 

The maximum refinery production rates and minimum customer demand rates are fixed and known to be as follows ... 

Many of PPG s high-pressure and high-temperature alarms are tested every six months. A significant number of the PPG Lake Charles Complex test frequencies have been developed using detailed reliability studies that consider the hazard rate (the acceptable probability of a process accident) and the demand rate (the number of times the critical alarm or shutdown function is required in service). [8]... 

The failure rates and demand rates of safety devices are considered low. 

Reorder point (ROP) = Demand rate (DR) x Lead time (LT) + Safety stock (SS)... 

The demand rate (DR) is the amount of producf used or sold wifhin a given period of time. It is expressed as the number of tmifs per xmif of time. The lead time (LT) is the amount of time it takes to order and receive a product from a supplier. In pharmacies the LT is often 1 day, it but can be upwards of 1 to 2 weeks, depending on the product and the supplier. The safety stock (SS) is the buffer of product kept on hand to accorranodate increases in demand or longer than expected LTs. 

When designing a work cell, you need two key pieces of information—the customer demand rate and the time the process takes. With this data, you can determine takt time—the rate at which you must produce in order to keep up with demand. 

In our example, RayRay gathers this data by visiting other beauty salons to see how many customers come in during a given period. He does this several times, on different days of the week, and during different times of the day to determine customer demand rate. To determine process cycle time, RayRay times several customers as they go through each step in the process (customer check-in, shampoo, hair cut, and payment). 

Once you have the customer demand rate (DR) for your product or service, and the cycle time (CT), you can determine the number of resources (NR) needed to maintain takt time by using two simple formulas ... 

For example, RayRay s research shows that the demand rate for hair cuts is one customer every hve minutes (DR = 1/5, so the takt time is 5 minutes). The cycle time for a hair cut (not including check-in, shampoo, or payment) is 15 minutes [NR = (1/5)(15) = 3]. So, RayRay s would need three resources, or stylists, to maintain takt time and keep up with customer demand. 

If the demand rate, 8, is the number of occasions per year that the protective device is actuated, then the hazard rate, or number of occasions per year when a hazardous condition exists, rj, is... 

Laboratory test data for a trip system shows a failure rate of 0.2 per year. If the demand rate is once every 2 years and the test interval is 6 months, what is the hazard rate Should a parallel system be installed ... 

Demand rate (number of occasions per year that a safety system is actuated)... 

Figure 13.2 shows domestic vanadium production and consumption 1960 to 1968, and the domestic maximum and minimum forecast demand for vanadium from 1968 to the year 2000, as estimated by Griffith. Cumulative requirements at the maximum demand rate from 1968 to 2000 are 520,000 short tons of vanadium. 

H16 has been measured in Warburg vessels (Eberhardt, 1965). It amounts to ca. 3000 (tl Hi-Oj-COj-mixture/hour/mg protein, when the partial pressure of oxygen is equal to that in the air (0.2 at). This gas uptake rate corresponds approximately to an oxygen demand rate of 0.661 02/hour/g dry weight. A suspension of 10 g cell dry weight per liter will, therefore, consume 6.61 oxygen or nearly 300 mmoles oxygen per hour. 

Suppose now that there are r types of items produced on a common single machine. The demand rate for type i, i = 1,. . . , r, is Aj. The service time distribution is identical for till types and has an exponential distribution with mean 1/p,. Suppose that there is a taiget stock level of z, for type i. Then define p by p = Aj/(p — The service level for type i is then given by... 

Again there are r classes with the target stock z, for class i, i = 1,2,. r. Demand rate for class i is A while aU types are produced on a single machine with the same service time distribution. It is possible to show that the probability of observing the number of jobs of each type in the machine queue of Uj, n, . n, . n,.is given by... 

The context is the following An inventory mtmager faces a constant demand rate that has to be satisfied from inventory. Ordering costs entail a fixed cost per order. Inventory held in the system incurs a holding cost. An inventory policy determines the quantity and frequency of orders. Each inventory policy has an associated cost to the organization. The two components of an inventory policy are ... 

While the EOQ model provides quick estimates of optimal behavior, it requires knowledge of the costs described earlier. It also requires us to have a good estimate of demand rate. However, the benefit of the model is that it is robust to variation in the assumptions. This is indicated as follows ... 

Typically, it can be assumed that the market value of (basic) chemicals increases with passing more processing steps. Hence, stock holding costs increase, too. The net demand rates provided in tons per day for Naphtha, Pygas, and Benzene under normal processing conditions can be found in Table 3.9 accompanied by stock holding cost rates in per ton... 

Table 3.9 Net demand rate lVs and holding cost rates for both scenarios...

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