The limit switch AD-MK 350 GVD serves the switching of limiting values on analogue signals, transmitter signals and resistance thermometer. If a 2-wire transmitter is connected, it will be supplied directly through a galvanic separated and current limited supply voltage. The device has analogue inputs for current, voltage and resistance thermometer, which can be utilised alternatively. The AD-MK 350 GVD can switch maximally two independent limiting values with its two potential-free change-over contacts. The switching thresholds and operating modes can be freely parameterized. This can be carried out via the optional control panel AD-VarioControl or via the programming software AD-Studio. The status of the relevant relay is indicated via LED at the front or at the operating module AD-VarioControl.



Switching limit values to active analog signals, 2- / 3-wire transmitters, and resistance thermometers, e.g. Flows, heights or temperatures.

Specific characteristics

  • bipolar current input (+/- 0.5 mA to +/- 50 mA)
  • bipolar voltage input (+/- 1 V to +/- 100 V)
  • power supply of 2- / 3-wire transmitters
  • two potential-free change-over contacts
  • operating module as an accessory
  • 23mm narrow housing with detachable terminal clamp

Business data

Order number
Vario - Limit Switch AD-MK 350 GVD
Accessory (optional)
Operating module AD-VarioControl
USB programming adapter AD-VarioPass
Configuration software AD-Studio
EClass 27210122
Customs tariff number / country of origin 8538 90 91 / Deutschland


Data sheet pdf en-mk350gvd.pdf (246 kB)
Operation manual VarioControl pdf man-variocontrol-ad-en.pdf (1 MB)
Tender text zip (10 kB)
Safety instructions pdf ad-safety-instructions.pdf (43 kB)

Technical specifications

Input current
Measuring range -50 ... + 50 mA DC
Input resistance 40 Ohm
Resolution 16 Bit
Accuracy 0,1 % of full scale
Input voltage
Measuring range -100 ... + 100 V DC
Input resistance 1 MOhm
Resolution 16 Bit
Accuracy 0,1 % of full scale
Transmitter supply
Off-load voltage 24,5 V
Voltage at 20mA 17,5 V
Current limit ~ 25 mA
Resistance thermometer inputs Pt100, Pt500, Pt1000 to DIN EN 60751
Measuring range -200 ... +850 °C
Connection method 2-, 3- oder 4-wire system
Resolution 16 Bit
Accuracy 0,6 K
Smallest measuring spans 20 K
Max line resistance 1) 10 Ohm/cable
Sensor supply 310 µA
1) With 2-conductor the line resistance comes as an offset into the measurement.
Resistance thermometer inputs Ni100, Ni500, Ni1000 to DIN EN 43760
Measuring range -60 ... +230 °C
Connection method 2-, 3- oder 4-wire system
Resolution 16 Bit
Accuracy 0,6 K
Smallest measuring spans 20 K
Max line resistance 1) 10 Ohm/cable
Sensor supply 310 µA
1) With 2-conductor the line resistance comes as an offset into the measurement.
Relay outputs A/B
Contact type Potential free changeover
Max. AC-breaking capacity 250 V AC, 2 A AC, 50Hz
Max. DC-breaking capacity 50 V DC, 2 A DC
Switching operations
Mechanical 107
AC: 230V / 2A, cos(phi)=1 6 * 105
AC: 230V / 2A, cos(phi)=0,4 2 * 105
DC: 24V / 1A 2 * 105
Transmission behaviour
Rise time 500 ms (output auf 90 %)
Temperature influence +/- 100 ppm/K of full scale
Voltage range AC 50 ... 253 V AC, 50/60 Hz
Nominal voltage AC 230 V AC
Voltage range DC 20 ... 253 V DC
Nominal voltage DC 24 V DC
Power consumption AC / DC 4 VA / 2,4 W
Dimensions (WxHxD) 23x110x134 mm
With operating module (bxhxt) 23x110x138 mm
Type of protection IP 20
Connection method Detachable terminal clamp
Terminals, wire cross section 2,5 mm² flex wire / 4 mm² one wire
Bolting torque terminals 0,5 Nm
Weight ~ 150 g
Manner of fastening 35 mm DIN rail 35mm
Environmental conditions
Ambient temperature -10 ... 50 °C
Storage and transport -10 ... 70 °C (no condensation)
Product family standard 1) EN 61326-1
Emitted interference EN 55011, CISPR11 Cl. B, Gr. 1
1)During electromagnetic disturbance minor changes in output signal are possible.
Electrical safety requirements
Product family standard EN 61010-1
Overvoltage category II
Pollution degree 2
Galvanic isolation, test voltages
Input/output 2,5 kV (1 min)
Signal/auxiliary voltage 3 kV (1 min)

Block and wiring diagram




CAD / CAE Daten

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Display and operating elements

On: LED for operating display in green
on - normal operation
flashing - Signal failure, signal outside range limits
Rel: two LEDs for relays A and B in red
on - relay activated

AD-PC: Communication interface for configuration by a PC

Communication interface for VarioControl

Modbus Communication

The optional AD-VarioConnect operating module has an RS-485 interface. The data is transferred via the Modbus RTU protocol, the AD-VarioConnect operating module represents a Modbus slave. Communication takes place according to the master-slave procedure and starts with a request from the master, e.g. from a PLC or a PC. Each bus participant must have a unique address. If a slave detects that its address has been addressed by the master, the slave always sends an answer. The slaves never communicate with each other. They are also not able to start a communication with the master.
The Modbus master can read out the individual registers of the AD-MK 350 GVD via the addresses.
The default standard data format is 19200,e,8,1 with slave address 1. These settings can be changed via the AD-VarioConnect operating module.

Start address Number of registers Name Unit Data type read write

 Measured values:
40607 2 Input signal mA / V / Ohm 7 1 0
40609 2 Scaled input °C / ? 7 1 0

Legend of the datatypes:
U08: 1 S08: 2 U16: 3 S16: 4 U32: 5 S32: 6 float: 7

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