What Is a Digital Frequency Meter? Housing Types and Selection Criteria
A digital frequency meter is a panel-mount measuring device that shows the frequency of the AC line it is connected to in hertz (Hz) on a numeric display.
A digital frequency meter is a panel-mount measuring device that shows the frequency of the alternating current (AC) line it is connected to in hertz (Hz) on a numeric display. It is used in generator, transfer, UPS and distribution panels to monitor whether the frequency deviates from 50 Hz. Compared with a pointer model, the decimal value is read directly and small deviations are not missed. It only measures; it is not a frequency inverter that adjusts motor speed. For a comparison of analog and digital types, see the parent Frequency Meters category.
Housing types
| Housing | Mounting | Model in the catalog |
|---|---|---|
| 36 × 72 mm | Front of the panel door | Tense DJ-F36 |
| 48 × 48 mm | Front of the panel door | Tense DJ-F48 |
| 48 × 96 mm | Front of the panel door | Entes EFC-3-48 |
| 96 × 96 mm | Front of the panel door | Tense DJ-F96 |
| Size not in name | Panel mount | Tense DJ-F72 |
| DIN rail housing | Inside the panel, on the same rail as the breakers | Tense DF-DIN |
| Size not in name | LED display | Schneider Electric METSEGLDM1132 |
Selection criteria
- Mounting location: If the value must be read without opening the door, choose a door-mounted model; if monitoring inside the panel is enough, choose a DIN rail model. For door models, the panel cut-out is smaller than the front bezel; take the size from the datasheet.
- Measuring input: The voltage to be measured (230 V phase-to-neutral or 400 V phase-to-phase) must be within the input range. Tense's DJ-V/DJ-F series manual gives a 1–400 Hz measuring range and a 15–500 V AC measuring input for DJ-F models; among the product names, only the DJ-F72 states this value. The Entes EFC-3-48 product name states 230 V AC and 20–400 Hz; check in the datasheet whether the 230 V is the supply or the measuring input.
- Supply: The measuring input and the device's auxiliary supply may not be the same terminals. A model powered from the line it measures goes dark when the line is lost; on a model with a separate supply, follow the wiring diagram.
- Display: A 3-digit display can show values around 50 Hz in steps of at most 0.1 Hz (50.0). For panels read from a distance, choose a larger housing with bigger digits.
- Accuracy: Among the product names, an accuracy value is stated only for the Schneider Electric METSEGLDM1132 (0.2%); where precise monitoring is needed, check the value of the other models in their datasheets.
Common mistakes
- Wiring only the measuring input on a model with separate supply terminals: The display stays dark; connect the supply terminals as shown in the diagram.
- Cutting the hole to the bezel size: The hole ends up too big and the device does not hold in the door.
- Monitoring two sources with one frequency meter in a transfer panel: To see mains and generator frequency at the same time, fit a separate frequency meter for each source.
Brands in the catalog
The Digital Frequency Meters category has 7 active products: Tense 5 (DJ-F36, DJ-F48, DJ-F72, DJ-F96, DF-DIN), Entes 1 (EFC-3-48), Schneider Electric 1 (METSEGLDM1132). The Entes and Schneider Electric models are sold on a quotation basis. To see frequency together with voltage and current on one device, see the Panel-Mount Multimeters category; confirm frequency measurement in the product datasheet.
Frequently asked questions
Does a digital frequency meter measure 60 Hz?
Yes. The measuring ranges in the catalog (1–400 Hz and 20–400 Hz) cover both 50 Hz and 60 Hz.
Should I choose DIN rail or panel mount?
Choose a panel-mount model if the value must be read with the door closed; choose a DIN rail model such as the Tense DF-DIN if monitoring inside the panel, on the same rail as the breakers, is enough.
Does a digital frequency meter need a separate supply?
It depends on the model. Some are powered from the line they measure, others have separate supply terminals; see the wiring diagram in the product datasheet.
What size should the panel cut-out be?
The cut-out is smaller than the front bezel and varies by model; use the cut-out size given in the product datasheet.