Patent GB-474478-A (GB)
Title: Apparatus for comparing the speed of two periodical processes
IPC: G01P3/56
Filed: 1936-07-17
Abstract: 474,478. Automatic control systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. July 17, 1936, No. 19881. Convention date, July 20, 1935. [Class 38 (iv)] [Also in Groups XXXVI and XVIII] Speed.-Apparatus for comparing the speed of two periodical processes comprises a first armature which is rotated under control of one of the processes, and a second rotatable armature connected to an indicating member and arranged to be magnetically coupled to the first armature by means of a magnetic flux from a winding which is fed with impulses transmitted under control of the second process. A synchronous motor 1, Fig. 1, driven from the supply mains, the frequency of which is to be indicated or controlled, drives an armature 5 having two oppositely arranged poles 7, within which is arranged an armature 6 having similarly arranged poles 8. A master clock sends impulses to a winding 14 arranged on an iron frame 4 around the armatures 5, 6. The impulses tend to rotate the armature 6 to a position such that when the impulses arrive the poles 7, 8 are opposite one another, at which point the reluctance of the magnetic circuit is a minimum, so that if the frequency of the mains supply varies a pointer 11 coupled to the armature 6 and moving over a scale 12, graduated in seconds, rotates for each impulse through an angle which is proportional to the change of frequency. The pointer 11 thus indicates at every moment the difference between the time indicated by the master clock and that indicated by a synchronous clock connected to the network. The pointer 11 may be combined with a contact device for automatically effecting corrections when the difference exceeds a certain value. A device is also provided for correcting the number of impulses transmitted to the indicator in the event that the master clock gains or loses. This consists of a selector, Fig. 3, provided with two groups of contact A B, and two stationary contact bars B, E, of which the bar B is connected by the line 28 to the indicating device. When the master clock has gained or lost, a correcting process is started by depressing a key 25, whereby the circuit of a relay 18 is energized and this energizes the driving magnet 20 for stepping on a contact member, which normally connects the contacts 1 of the groups A, D to the bars B, E, to the position 2. The contact member remains in this position until an mpulse from the master clock energizes a relay 16, which closes a contact 171 and transmits an impulse through the contact 2 and the bar B to the line 28, and also re-energizes the relay 18 for energizing the stepping-on magnet 20 for the contact member, which moves to the position 3. A switch 22 is manually engaged with contact 23 or 24 according as the main clock is slow or fast. If the former is the case, the contact member after moving to position 3 automatically moves on from contact 3 to contact 11, the speed being approximately ten steps per second. At contact 10 an impulse is transmitted to the line 28 and the contact member remains at contact 11 until the next impulse from the master clock arrives, when it is automatically moved on to contact 18 at which it stays until other impulses move it on first to contact 23 and finally back to contact 1. During this movement, further impulses are transmitted to the line 28 at contacts 17, 22, 25 and again at contact 1. By this means for four impulses from the master clock five impulses are transmitted to the line 28, so that if the former is one second slow, the indicator is corrected. If the main clock is one second fast, the contact 24 is engaged and the contact member of the correcting mechanism is stepped on as before transmitting an impulse at contact 12 corresponding to an impulse from the master clock at contact 11. Another master-clock impulse moves the contact member from contact 18 to contact 19, and the impulse which it then transmits to line 28 lasts while it moves over contacts 20, 21, 22, 23. It stays at the latter until the next master-clock impulse arrives when it moves back to contact 1, and during this period which lasts for practically one second (the interval between the masterclock impulses) the armatures 5, 6 are magnetically coupled together and the armature 6 rotates through an angle sufficient to move the pointer 11 backwards through one second, thus correcting the indicator. By repeating either of these processes, a loss or gain of several seconds may be corrected. In series with the conductor 28 there can be arranged a stepping mechanism for operating a secondary clock which will also be corrected at the same time as the indicator 11 is corrected.