The following is my understanding. Please contact me with corrections. On modern ship's, the engine(s) are controlled directly from the bridge. For older ships, the desired setting were transmitted to the engine room and carried out by the engineers. The ship's order telegraph connects the bridge with the engine room. The desired action is set by moving the handle to, for example, Full Ahead. The pointer on the engine rooms telegraph is moved to that setting. After the order is carried out, the handle on the engine room telegraph is moved to the new setting. This moves the pointer on the telegraph on the bridge. March 12, 2021 Paul Slotsema, a graduate of King's Point Merchant Marine Academy with a lot of practical experience, offered the following comments: "Dave, That captures the operation well. It might be interesting to add that engine order telegraphs are also known as Chadburns after the company in Liverpool who first started making early versions. Also, an engine order such as slow, half, or full ahead is also commonly referred to as a bell: slow bell, half bell, or full bells. This is due to the operation of the EOT with the bell ringing to indicate a change in engine order. One minor note of clarification is that the engine room aligns their handle to the Bridge's pointer once the bridge's order is acknowledged, not necessarily carried out. This applies mostly to manually controlled steam propulsion systems where engineers would have to physically adjust turbine governors, pumps, and boilers to bring the plant to the desired revolutions which could take quite a while. Thus the engine order would be acknowledged and then the work would begin. Again, brings back great memories! Respectfully, Paul Slotsema" Charles Henshel patented an early version of the ship's order telegraph in 1921. This required no external power, but had a crank to generated the electricity required. I don't know when the version of or unit was developed, but am guessing that it was about the time of WWII. I can't locate another patent. Our unit uses synchro's to transmit the information. These are ingenious devces that are powered by alternating current. They have 3 electromagnets spaced 120 degrees apart and a central rotor. Wikipedia explains: "A synchro (also known as selsyn and by other brand names) is, in effect, a transformer whose primary-to-secondary coupling may be varied by physically changing the relative orientation of the two windings. Synchros are often used for measuring the angle of a rotating machine such as an antenna platform. In its general physical construction, it is much like an electric motor. The primary winding of the transformer, fixed to the rotor, is excited by an alternating current, which by electromagnetic induction, causes voltages to appear between the Y-connected secondary windings fixed at 120 degrees to each other on the stator. The voltages are measured and used to determine the angle of the rotor relative to the stator." Wkipedia includes these diagrams:   The US Navy has a much more complete explanation. Among other uses, the Navy used this technology to aim large guns. There are apparently ways to obtain accuacy of well under 1 degree. Our telegraph had a partial wiring diagram under the access panel. Here is an enhanced image: 
and a detailed spreadsheet. The "bell" that Paul refers to is an electric bell on the starboard side of the pedestal. There are 2 microswitches in the unit, activated by notches in a wheel connected to the main shaft. I assume that one switch triggered the bridge's bell, and the other the engine room's. The notches also serve as detents for the handle position. While sorting out the wiring, I measured the resistance across the two power inputs for the synchros, and was surprised that it was only about 10 ohms. Given Ohm's law, the current draw would have been 115/10 = 11+ amps, too much for the small wires. I figured this was related to the fact that the supply was AC, but didn't know the details. Paul's brother in law is Luke Raymond, a PhD in Electrical Engineering at Stanford, offered this explanation: "Hi Dave, Good to hear from you! The telegraph looks amazing, sounds like a great project. I don't have a ton of experience with synchronous motors but one thought is that the inductance of the motor windings is significant enough to present a high impedance under ac excitation. If so, you wouldn't be able to measure the 60 Hz impedance using an ohm-meter but would need an RLC meter or multimeter that can measure inductance. Thinking about 60 Hz transformers as an example, the dc resistance of the windings is very low such that if one were to apply a dc voltage across the transformer the current would quickly rise to an almost infinite value until something blows. However, the ac impedance is high enough to limit the winding current during the 60 Hz half-cycle to a reasonable level until the polarity reverses. One thing that might be worth trying if you're curious whether the motors are good is to apply 115 VAC to the power terminals with a very small slow-blow fuse in series. You could start small and gradually increase the current rating until you confirm whether or not they are functional without risking damage or fire :). Cheers, Luke" I have a pretty good understanding of analog electroncs, but not AC. I first tried 24 VAC with a fuse and clamp-on ammeter, and it did not register. I then tried 120 VAC, and recorded about 1 amp. Since I only have one telegraph, I will probably try connecting this unit's transmitting synchro to its receiving synchros. The telegraph also has a rotary switch that is geared to the shaft. The swich has 3 layers, one of which has wires connected to a terminal block. I don't know how this information was used, but I hope to connect the terminal block to a Raspberry Pi for some kind of display. It would be fun to synthesize the voltages for the synchros to simulate a response from the engine room, but that probably won't happen. |