The KOBOLD KFD2 and KFA5 are isolation switching amplifiers that transmit switching signals from NAMUR sensors or mechanical contacts in hazardous areas to control circuits in non-hazardous areas. Each unit provides an intrinsically safe input, line fault monitoring, and an SPDT relay output in a 20 mm (0.79 in) wide DIN rail housing. The KFD2 runs on 24 V DC and the KFA5 on 115 V AC; both come in single-channel and dual-channel versions.
How the KFD2 and KFA5 isolation switching amplifiers work
The amplifier feeds a low-power control circuit to a NAMUR proximity sensor or a dry contact in the field and switches its relay contact when the input current crosses the switch point. The input signal is isolated from both the output and the input power in accordance with DIN EN 60947-5-6 (NAMUR), and the output and input power are isolated from each other.
The input circuit operates with a floating voltage of approximately 8 V DC and a short-circuit current of approximately 8 mA. The switch point lies between 1.2 and 2.1 mA with a switching hysteresis of approximately 0.2 mA. Input pulses and interpulse periods must each be at least 20 ms. The relay responds after a delay of approximately 20 ms and supports switching frequencies below 10 Hz.
Input and output specifications
The input is intrinsically safe to NAMUR and EN 60947-5-6. The output is a single-pole double-throw (SPDT) relay contact that is not intrinsically safe, rated for loads up to 2 A with a service life of 10 million (10⁷) switching cycles.
- Input: NAMUR sensor or dry contact, intrinsically safe per EN 60947-5-6
- Maximum contact loading: 253 V AC / 2 A / cos φ > 0.7, or 40 V DC / 2 A resistive load
- Electrical isolation per IEC/EN 61010-1, rated insulation voltage 300 V rms
- Electromagnetic conformity: EN 61326-1 and NAMUR NE 21
Power supply options: 24 V DC (KFD2) or 115 V AC (KFA5)
The two models differ in power supply. The KFD2 is the 24 V DC version, with power consumption of 0.9 W or less and a permitted ripple of 10% or less. The KFD2, like other DC-powered K-System devices, accepts 20 to 30 V DC through its supply terminals or through a PowerRail insert in the DIN rail that also carries a collective error message. The KFA5 is the AC version, rated for 115 V AC ±10% at 60 Hz, with power consumption of 1 W or less.
Hazardous area ratings and intrinsic safety values
The control circuit is marked II (1) G [Ex ia] IIC and II (1) D [Ex ia] IIIC, with protection types EEx ia and EEx ib. The amplifier is associated apparatus installed in the safe area, and its intrinsically safe circuit can be led into the hazardous area. Maximum values of the intrinsically safe input circuit:
- Voltage U₀: 10.5 V (KFD2), 10.6 V (KFA5)
- Current I₀: 13 mA (KFD2), 19.1 mA (KFA5)
- Power P₀: 34 mW (KFD2), 51 mW (KFA5)
Line fault monitoring and LED status indication
The control circuit is monitored for line interruption (lead breakage, LB) and line short circuit (LK). A line current of 0.1 mA or less is evaluated as a line interruption and a current above 6 mA as a short circuit. When a line fault is detected, the switching output is switched to the de-energized state and the red LED signals the fault.
Three front LEDs follow the NAMUR NE 44 color convention: green for power, yellow for relay output, and red for LB/LK line faults. DIP switch S1 sets the mode of operation and switch S3 is assigned to LB/LK monitoring; switch S2 has no function on these models.
Mounting, wiring, and housing
The housing measures 119 × 20 × 115 mm (4.69 × 0.79 × 4.53 in), weighs 0.33 lb (150 g), and snaps onto a 35 mm DIN mounting rail per EN 60715. The Macrolon® (polycarbonate) case is rated IP 20 and meets fire protection class V2 per UL 94. Units can be mounted vertically or horizontally, side by side without spacing.
Detachable terminal blocks accept conductors up to 2.5 mm² (14 AWG), with terminal screws tightened to 0.5 to 0.6 Nm (4.4 to 5.3 lbf·in). The ambient temperature range is -4 to 140 °F (-20 to 60 °C), storage is -40 to 194 °F (-40 to 90 °C), and relative humidity is limited to 95% non-condensing.
Ordering: single and dual channel models
Four versions are available. In the model code, SR designates a switch amplifier with relay output and Ex1 or Ex2 gives the number of channels.
- KFD2-SR2-Ex1.W: 1 channel, 24 V DC supply
- KFD2-SR2-Ex2.W: 2 channels, 24 V DC supply
- KFA5-SR2-Ex1.W: 1 channel, 115 V AC supply
- KFA5-SR2-Ex2.W: 2 channels, 115 V AC supply
Common Questions about KFD2-KFA5 - Isolation Switching Amplifier
An isolation switching amplifier is an isolated barrier. It limits the current and voltage supplied to an intrinsically safe field circuit, electrically isolates that field circuit from the control side, and converts the switching state of the sensor into a relay contact the control system can read. The KFD2 and KFA5 do this for NAMUR sensors and mechanical contacts.
Power supply is the main difference: 24 V DC for the KFD2, 115 V AC ±10% at 60 Hz for the KFA5. Inputs, relay output, housing size, and channel options are the same. The two carry slightly different intrinsic safety maximum values: 10.5 V, 13 mA, and 34 mW for the KFD2, and 10.6 V, 19.1 mA, and 51 mW for the KFA5.
Yes. The input accepts either a NAMUR-type proximity switch or a dry mechanical contact. Each input state must be held for at least 20 ms, since the input pulse length and the interpulse period are both specified at 20 ms or longer. DIP switch S1 on the front of the unit selects the mode of operation.
Each output is a non-intrinsically-safe SPDT relay contact. It switches up to 253 V AC at 2 A with cos φ greater than 0.7, or 40 V DC at 2 A into a resistive load. The contact is rated for 10 million switching cycles, responds in approximately 20 ms, and handles switching frequencies under 10 Hz.
The amplifier watches the current flowing in the sensor circuit. A current of 0.1 mA or lower is treated as a broken or interrupted line, and anything over 6 mA signals a short circuit. Either condition is shown on the red LED, and line faults are kept from being interpreted as valid switching signals.
Both models are marked II (1) G [Ex ia] IIC and II (1) D [Ex ia] IIIC (protection types EEx ia, EEx ib). The amplifier itself sits in the safe area; only its intrinsically safe input circuit enters the hazardous area. Verify intrinsic safety by checking the field device against U₀, I₀, and P₀ under IEC/EN 60079-14.
The housing snaps vertically onto a 35 mm DIN rail to EN 60715; snapping it on from the side can damage the contacts. The removable, coded terminal blocks take leads up to 2.5 mm² (14 AWG) and are tightened to 0.5 to 0.6 Nm. Use only power supplies that protect against direct contact, such as SELV or PELV.
The units operate from -4 to 140 °F (-20 to 60 °C) in any mounting orientation and can be stored at -40 to 194 °F (-40 to 90 °C). The enclosure is rated IP 20 and withstands vibration of 10 to 150 Hz at 1 g (EN 60068-2-6) and shock of 15 g for 11 ms (EN 60068-2-27).
Green on means the power supply is OK; off means power failure or insufficient supply. Red on indicates an internal device fault, and red flashing an external line fault that needs inspection. Yellow on means the relay is energized, or the NAMUR sensor is undamped; yellow off means the relay is de-energized or the sensor is damped.
Product Specifications
Power
24 VDC (KFD2) or 110 VAC (KFA5)
Inputs
NAMUR or Dry Contact
Product Features
Single or Dual Channel Models Available
EEx ia IIC Control Circuit
Narrow, DIN-Rail Mounted Design
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