(4) Safety and operational assurance
Protection mechanism: The device supports password protection function, with a password range of 0... 999. It is disabled by default and can prevent unauthorized personnel from modifying device parameters when enabled; Equipped with a sealed transparent cover, it can protect the internal operating components, facilitate the viewing of equipment status, and meet the requirements of dust prevention and misoperation prevention; Equipped with continuous self-monitoring function, it can detect the working status of the equipment in real time. If there is a fault, it will be promptly reported through alarm lights and relays.
Operation buttons: including three core buttons: Test (T), Reset (R), and Menu (MENU). The functional reuse design balances convenience and integration:
Test key (T): Short press to switch the display of measurement values, and the menu can switch options up or modify parameters; Long press (>1.5 s) to activate the self-test function.
Reset button (R): Short press to switch the display of measurement values, and the menu can be used to switch down options or modify parameters; Long press (>1.5 s) to clear stored alarm records.
MENU: Short press to confirm, used to confirm the displayed measurement values or modified parameters; Long press (>1.5 s) to call up the menu system; Long press the ESC function (>1.5 seconds) to abort the current operation or return to the previous menu.
Indicator light status: Power light (ON, green): Always on when power supply is normal, flashing when system fault alarm is triggered; Alarm lights (AL1, AL2, yellow): keep on when triggered by corresponding alarm relays K1 and K2, and flash when the system fails; The indicator light status can quickly determine the working status and alarm situation of the equipment.
(5) Alarm output configuration
The equipment is equipped with two independent alarm relays (K1, K2), each designed with a single conversion contact, supporting switching between normally closed (N/C) or normally open (N/O) operating modes to meet different control circuit requirements.
The configurable monitoring types of relays include: Err, U<, U>, Asy, Hz<, Hz>, PHS, and S.AL. The factory default configuration is:
K1: Overvoltage (U>), asymmetry (Asy), normally open (N/O) mode.
K2: Under voltage (U<), asymmetric (Asy), normally closed (N/C) mode.
The electrical life of the relay reaches 10000 cycles, and the contact parameters comply with the IEC 60947-5-1 standard. The rated parameters under different usage categories are as follows:
Usage category: Rated voltage, rated current
AC-13 230 V 5 A
AC-14 230 V 3 A
DC-12 24 V 1 A
DC-12 110 V 0.2 A
DC-12 220 V 0.1 A
The minimum contact load is 1 mA when AC/DC ≥ 10 V, ensuring reliable operation in low load scenarios.

Model specifications and ordering information
(1) Core model parameters
The equipment is divided into two core models according to the power supply voltage, and each model provides two wiring options: screw terminals and push in terminals. The specific parameters are as follows:
Model Supply Voltage (Us) Frequency Range Terminal Type Product Number (Art. No.)
VMD420-D-1 AC 16... 72 V/DC 9.6... 94 V 15... 460 Hz screw terminal B93010005
Push in terminal B73010005
VMD420-D-2 AC/DC 70... 300 V 15... 460 Hz screw terminal B93010006
Push in terminal B73010006
Note: The power supply voltage is the absolute rated value, and actual use should be within the specified range to avoid overvoltage or undervoltage operation.
(2) Accessory information
Accessory Name Usage Product Number (Art. No.)
Fixed clamp for screw installation (1 per device) used for fixing equipment screws B98060008
Key technical parameters
(1) Insulation and voltage resistance performance
Project parameter specifications
Rated insulation voltage 400 V
Rated impulse voltage/pollution level 4 kV/III
Protective isolation (strengthened insulation) between A1, A2 and N, L1, L2, L3, 11, 12, 14, 21, 22, 24
Voltage withstand test (IEC 61010-1) (N, L1, L2, L3) and (A1, A2), (11,12,14): 3.32 kV
(N, L1, L2, L3) and (21,22,24): 2.21 kV
(A1, A2) and (11,12,14), (21,22,24): 2.21 kV
(2) Power supply and power consumption
Model Supply Voltage Range Frequency Range Power Consumption
VMD420-D-1 AC 16…72 V / DC 9.6…94 V 15…460 Hz ≤ 4 VA
VMD420-D-2 AC/DC 70…300 V 15…460 Hz ≤ 4 VA
(3) Measure circuit parameters
Project parameter specifications
Measurement range (true RMS) - L-N AC 0... 288 V
Measurement range (true RMS) - L-L AC 0... 500 V
Input impedance (L1-N, L2-N, L3-N) 1 M Ω
Input impedance (N line) None (n.a.)
Rated frequency (fn) 15... 460 Hz
Frequency display range 10... 500 Hz
(4) Environment and EMC Performance
Electromagnetic compatibility (EMC): Complies with EN 61326-1 standard, has strong resistance to electromagnetic interference, and is suitable for complex industrial electromagnetic environments.
Temperature range:
Working temperature: -25...+55 ℃
Transportation temperature: -25...+70 ℃
Storage temperature: -25...+55 ℃
Classification of climatic conditions (IEC 60721):
Fixed use (3K23): no condensation, no icing
Transportation (2K11, 1K22)
Long term storage (1K12)
Email:wang@kongjiangauto.com