Micro digital panel meters, digital counters and 6-digit remote display offer a choice of two high-frequency switching power supplies. These provide stable, isolated power for instrument operation plus excitation outputs at a substantially reduced weight and over a broader range of input voltages and power frequencies than conventional linear supplies.
High voltage AC or DC power. The standard Micro supply accepts power from 85 to 264 Vac, 47 to 440 Hz. This allows the same meter to operate worldwide without modification. The supply also accepts 90 to 370 Vdc.
Low voltage AC or DC power. An optional low voltage supply operates from 9 to 37 Vdc or 8 to 28 Vac, 47 to 440 Hz. This supply allows the Micro to be powered from batteries or from 28 Vac, 400 Hz aircraft power.
Isolated Excitation Output
Each power supply provides three jumper-selectable, isolated excitation outputs: 5 Vdc at 100 mA, 10 Vdc at 120 mA, or 24 Vdc at 50 mA. These outputs can be used to power external sensors, transmitters and up to four 350 ohm load cells, thereby avoiding the need for an expensive external supply. When powering a load cell or potentiometer, a ratiometric operating mode can be selected, where the meter monitors the excitation supply and removes the effects of voltage variation.
In addition to the isolated excitation output, regulated 5 Vdc at up to 50 mA is brought out and can be used to power external logic.
Wiring of Excitation Output
4-wire, 4-20 mA transmitter wiring
2-wire 4-20 mA transmitter wiring
With four-wire transmitters, two wires are used to apply 10 or 24 Vdc, and two separate wires are used to sense the transmitter’s 4-20 mA output.
With two-wire transmitters, the same two wires are used to power the transmitter and carry the 4-20 mA output, which is made to flow across an internal 10 ohm resistor between pins 3 and 4.
Both power supplies and their connectors (standard) are designed to UL/IEC/CSA safety standards. The two Micro power supplies also do double-duty by providing two connector inputs (A & B) and a digital ground for signals such as meter hold, reset, tare, etc. These signals do not affect power supply operation.
95-240 Vac ±10% or 95-370 Vdc
12-34 Vac or 10-48 Vdc
DC and 49-440 Hz
5.3 W max
Excitation Power Supply
5 Vdc ±5%, 100 mA max
10 Vdc ±5%, 120 mA max
24 Vdc ±5%, 50 mA max
50 mVp-p max
Isolation to power ground
Safety-rated to 250 Vac, 4.2 kVp per High Voltage Test