QPL-approved Power Monitors designed to meet the requirements of MIL-STD-704 for aircraft and missile applications. Provide solid-state sensing of over or under voltage, over or under-frequency, and phase sequence condition of 115V, 400Hz power sources.

The BC Systems Series 94152 Power Monitor is a sensing device designed for installation in aircraft. It senses the output characteristics of the 115V, 400Hz ground power source and protects the aircraft’s AC distribution system and equipment from over or under-voltage, over or under frequency, or improper phase sequence. The output of the Power Monitor controls the coil circuit of the aircraft’s AC contactor. Any out of specification condition will reenergize the contactor. (See External Circuit Diagrams on the other side of this sheet.)

Two standard models are offered: BC Systems Model 94152-2 and 94152-4 (MIL Part No. M24021-2 and M24021-4 respectively). The principal difference between the two models is that the -2 output is a nominal 26VDC between connector pins 4 and 5, while the -4 output is a switch closure between pins F and H. Other differences are shown below:

Weight, max.
26 :t4VDC
2.5 Ibs.
Switch Closure
2.0 Ibs.

BC Systems Series 94152 Power Monitors are completely solid-state devices employing all military-approved components. They sense the condition of a 115V, 400Hz power source and determine its acceptability in terms of MIL-STD-704. If the condition of the 115V, 400Hz input power varies from the specified limits, the Power Monitor’s output circuit will open and remain open until reset. The output circuit can be used to drive an AC contactor or any other control device.

The functional block diagram shown below illustrates the operation of the Power Monitor modules:

  • If the input power is not phase A.B.C. or B.C.A. the output will not be actuated.
  • If the input voltage is over or under frequency, the timer T2 will start and the output will deactuate after 1 second if the frequency has not returned to the specified range.
  • If the input voltage is above 130 volts or below 100 volts the timers T1 and/or T2 will start and time out proportionate to the degree of deviation from the nominal, in accordance with the voltage transient curve of MILSTD-704 (See other side of sheet).


BC Systems also produces a complete line of related products such as special purpose power monitors, voltage sensors, frequency sensors, phase detectors, and electronic timers. For complete information, contact. BC Systems directly or through the local sales representative.

BC Systems Inc., is a designer and manufacturer of military power supplies, using the latest solid state device technology to achieve reliable specification compliant products. Power supplies are designed to meet or exceed customer specified environmental requirements. Military applications include all service platforms: ground, air and shipboard. Power supply technical qualifications are based on our vast experience in the design and manufacture of power supplies.

BC Systems Inc employs innovative packaging and thermal management techniques which are manufactured onsite providing enhanced production process control. Our complete in-house manufacturing capability provides our design and manufacturing team with the advantage of supplying products that achieve maximum performance, in the smallest package possible, within schedule requirements.

BC Systems is a small, Veteran owned business serving the U.S. Government and U.S. Military for over 30 years. BC Systems’ specializes in Military Power Supplies and Airborne Power Control Products.