The current control system includes a buffer amplifier for the actual current value. This makes it possible to connect a meter to display the armature current, for example. By applying a control signal, the output of the buffer amplifier can be converted, so that the output signal changes sign when the direction of current flow changes in a double convertor.
37 3
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Double convertors have blocking circuits which switch the control pulses to the correct thyristors to give the required direction of the current flow. The input signal for the blocking circuits is the total current reference.
When the direction of current flow changes, the output voltage of the convertor is automatically matched to the armature voltage of the dc machine, so that current begins to flow immediately. This arrangement saves the time that would otherwise be needed to drive the current controller to the control voltage that gives through the machine.
38 6
Dwell on thyristor convertors with your fellow-student. Use ex. 36, 37.
Home exercise. Read the words, explain the function of their suffixes and prefixes. Give Russian equivalents for them:
REmove, careFULLY, installaTION, exactLY, ventilatING, openING, deterioraHON, resistANCEs, housING, insulaTION, OVERload, excess-IVE, connecTION, PREmature, rotaTION, failURE, maintenANCE, RE-newING, Disassemble, REplace, useLESS, internAL, pressURE, abra-SION, withIN, withOUT, sufficiENT, inspecTION, DEfault, REset, UNDERcurrent, UNtapped, considerABLY. machinERY, equipMENT, relationSHIP, comprehensIVE, hardWARE, reliabillTY, surveillANCE, UNused, softWARE, REbuildING, invertER, triAL, personnEL, ANTI-vibration, OVERall, Alive, ENcourage, transmisSION, Alike, domestic, throughOUT, AFOREmentioned, MISused, COUNTER-voltage.
40 20
Home exercise. Read the text and write out the names of main parts of a vacuum cleaner. Describe the steps taken by the psychiatrist in his treatment. What is your opinion of labour-saving devices?
Labour-Saving Devices
Quite a crowd had gathered in front of the local hospital. Presently the white door opened and Doctor Curewell himself appeared there. His voice sounded loud and clear when he said addressing the crowd:
— He’s gone to nuts, thinks he’s a vacuum cleaner!
— Poor old James, — murmured many voices.
You see, James Parker had a small workshop and was said to be able to mend anything from a coffee mill to a TV set. Whenever anything went wrong it was James that people went. They found him always in his workshop with a drill or a hammer in his hand, always smiling and always ready to help.