Time-proportioning power controller

A relatively inexpensive, time-proportioning power controller is the mercury contactor. With this switch, there is no zero-crossing detection, so there will be some noise in the circuit when the contactor is turned on and off. 

It is clear that SCR power controllers can also be used for time proportioning power control by increasing the cycle time. However, this type of use does not utilize the inherent advantages of the SCR power controller. 

The power consumption of the barrel and die heaters can be determined by measuring voltage and current to the heater. This works well in current proportioned temperature control. It does not work well with on-off control or time-proportioning temperature control. In the latter case, a wattmeter should be used with a power integrating function. In this case, the integrated power over a certain time period can be measured so that the average power consumption of the barrel heater can be established. Commercial extruders generally do not have sufficient instrumentation... 

This problem can be avoided by using a zero-crossover-fired power controller. This is a time-proportioning system controlled by the temperature controller. Being zero-voltage fired, this controller s circuit is free of RF noise. In other words, the switching occurs when no voltage is on the line. 

An oven is typically used for the purpose of controlling temperature. Crystal resonators reside inside the oven with the oscillator control circuitry either internal or external to the oven. When the circuitry is externally connected, stabihties in frequency of 5 parts in 10 are possible. For internal circuitry, stabilities of several parts per billion have been obtained in proportionally controlled ovens. Improved frequency-temperature stabihty can also be obtained with two-stage ovens. Usage of ovens is limited, however, by the disadvantages that arise such as required warmup time, high-power consumption, large volume, and reduced component rehability when frequent on/off cychng of the oven occurs. 

PrImary-Voltage-Control-AC Motor Driver. Induction motor torque at any slip s is proportional to primary V. Rotor-power dissipation is equal to s times the air-gap power. These two relationships define the boundary of operation of an induction motor with primary voltage control of speed. As the speed is reduced (s increased) at constant torque, the air-gap power remains fixed, but the power divides between rotor circuit dissipation and mechanical shaft power. 

The idea of a root locus plot is simple—if we have a computer. We pick one design parameter, say, the proportional gain Kc, and write a small program to calculate the roots of the characteristic polynomial for each chosen value of as in 0, 1, 2, 3,., 100,..., etc. The results (the values of the roots) can be tabulated or better yet, plotted on the complex plane. Even though the idea of plotting a root locus sounds so simple, it is one of the most powerful techniques in controller design and analysis when there is no time delay. 

Power proportioning controllers are generally more sophisticated forms of the constant voltage units, employing solid state circuitry and rapid time-constant sensing circuits. An isolation transformer isolates the controller from line voltage fluctuations. If adequate insulation of the column from ambient air changes is provided, the controllers can be quite accurate. 

Many manufacturers have used the capabilities of on-board processing power to provide a user friendly interface for the operator. This results in a host of useful (and some not so useful) features for the analyst, and allows the pump to be remotely controlled by a computer, or another component of the HPLC system. This can facilitate method development for instance, as the pump can be programmed to change automatically the composition of the mobile phase after a number of runs. It does this by changing the proportion of time that it draws from each of a number (up to four) of solvent reservoirs, that can contain diflferent modifiers or buffers. Computerisation of pumps can also allow unattended runs to be performed with a greatly increased measure of confidence. In a networked... 

---