Pendulum-and-hydrostat control is a control mechanism developed originally for depth control of the Whitehead torpedo. It is an early example of what is now known as proportional and derivative control. The

hydrostat A muscular hydrostat is a biological structure found in animals. It is used to manipulate items (including food) or to move its host about and consists mainly of muscles with no skeletal support. It performs its hydraulics, hydraulic movement with ...

is a mechanism that senses pressure; the torpedo's depth is proportional to pressure. However, with only a hydrostat controlling the depth fins in a

negative feedback Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused ...

loop, the torpedo tends to oscillate around the desired depth rather than settling to the desired depth. The addition of a

pendulum A pendulum is a device made of a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate i ...

allows the torpedo to sense the pitch of the torpedo. The pitch information is combined with the depth information to set the torpedo's depth control fins. The pitch information provides a damping term to the depth control response and suppresses the depth oscillations.

Operation

control theory Control theory is a field of control engineering and applied mathematics that deals with the control system, control of dynamical systems in engineered processes and machines. The objective is to develop a model or algorithm governing the applic ...

the effect of the addition of the pendulum can be explained as turning the simple proportional controller into a proportional-derivative controller since the depth keeping is not controlled by the depth alone anymore but also by the

derivative In mathematics, the derivative is a fundamental tool that quantifies the sensitivity to change of a function's output with respect to its input. The derivative of a function of a single variable at a chosen input value, when it exists, is t ...

(rate of change) of the depth which is roughly proportional to the angle of the machine.Bennett, "A History of control engineering: 1800-1930" The relative gain of the proportional and derivative functions could be altered by adjusting the linkages. It was mainly used to control the depth of

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

es until the end of the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

, and it reduced depth errors from ±40 feet (12 meters) to as little as ±6 inches (0.15 m). The pendulum and hydrostat control was invented by Robert Whitehead. It was an important advance in torpedo technology, and it was nicknamed "The Secret".

References

External links

* https://archive.today/20120530070555/http://www.btinternet.com/~philipr/torps.htm * {{cite journal , last=Milford , first=Frederick J. , title=U.S. Navy Torpedoes: Part One: Torpedoes through the thirties , date=April 1996 , location=Annandale, VA , journal=Submarine Review , publisher=Naval Submarine League , url=http://www.geocities.com/Pentagon/1592/ustorp1.htm , archiveurl=https://web.archive.org/web/20091023132602/http://geocities.com/Pentagon/1592/ustorp1.htm , url-status=dead , archivedate=2009-10-23 Control devices Mechanisms (engineering) Pendulums Torpedoes