How to Choose a Safety Door Switch / Interlock
A safety door switch (interlock) ties a movable guard — a door, gate, or hatch — into the machine's safety circuit. Open the guard and the hazardous motion stops; with a guard-locking version, the door additionally stays locked until the machine is safe to enter. It is the standard safeguard wherever people pass through a physical barrier occasionally rather than interacting with the machine every cycle.
The selection logic runs in a fixed order: first decide whether you need plain interlocking or guard locking; then the locking principle and holding force; then contact-type versus non-contact sensing; then the coding level against defeat; and finally contacts, wiring, and mechanical accessories.
This guide follows that order, using DAIDISIKE's DX family as concrete examples: the DX-D2/D3 mechanical door switches, the DX-W2/W3/W5 and DX-D6 guard-locking switches, the DX-C1 coded-magnet and DX-R1 non-contact switches, the DXL door bolt, and the DX-K key/actuator system.
Door Switch or Door Lock: Do You Need Guard Locking?
The first question is about your machine's stopping behavior. If the hazard stops essentially immediately when the door opens, a plain interlock switch is enough: it detects the open door and drops the safety circuit. The DAIDISIKE DX-D2/DX-D3 is this type — a mechanical contact interlock with NC/NO contacts and no locking function, with forced (positive) contact separation at ≥60 N over ≥10 mm of travel so a welded contact cannot fake a closed-door signal.
If the machine has run-down time — spinning spindles, coasting fans, presses finishing a stroke — or if an interruption mid-cycle would wreck the process, you need guard locking: the door physically cannot open until the control system releases it. DAIDISIKE's guard-locking options are the DX-W2, DX-W3, and DX-W5 solenoid door locks and the DX-D6 compact guard-locking switch.
A third option covers full-body-access doors: the DXL safety door bolt is a purely mechanical slide bolt (48 mm bolt travel, door gaps 1–10 mm, rated 1,000,000 operations) whose base directly accepts DX-W2, DX-W3, DX-D2, or DX-D3 switches — combining a robust handle mechanism with the electrical interlock in one assembly.
Step 1: Power-to-Release or Power-to-Lock?
Guard-locking switches come in two locking principles, and the choice follows from your risk assessment, not preference.
Power-to-release (mechanically locked, solenoid released — DAIDISIKE code GC, or the DX-D6 C-type): a spring holds the lock; energizing the solenoid releases it. On power failure the door stays locked. This is the usual choice when the hazard is the machine itself, because a power cut must not let anyone walk into a coasting mechanism. Plan an escape/maintenance release strategy for people who could be locked inside a cell.
Power-to-lock (solenoid locked, mechanically released — code GD, or the DX-D6 D-type): the solenoid holds the lock only while energized; power failure unlocks the door. This suits processes where being locked in is the greater danger, or where the process protection (not personnel protection) is the reason for locking. The DX-W2, DX-W3, and DX-W5 are all offered in both GD and GC versions, and the DX-D6 in both C and D types, so the electrical and mechanical design carries over whichever way the risk assessment lands.
Step 2: How Much Holding Force Does the Door Need?
Holding force is what stops a person from simply pulling the locked door open. Size it against the realistic pull a person can apply to your door geometry — a large door with a long lever arm needs more margin than a small hatch.
The DAIDISIKE DX-W2, DX-W3, and DX-W5 are each rated at 1300 N holding force; the DX-D6 raises this to 2000 N. As a sanity check, a determined adult pulling with both hands can exceed several hundred newtons, so four-digit holding forces are the norm for walk-in cells.
Also check the solenoid supply: the DX-W2 solenoid runs on 24 V DC ±10% at roughly 200 mA (4.8 W); the DX-W5 additionally offers a 10–115 V AC/DC solenoid option for mixed-voltage retrofits. Mechanical life matters on high-traffic doors — the DX-W2 is rated 1,000,000 mechanical operations (150,000 electrical).
Step 3: Contact-Type or Non-Contact Sensing?
Contact-type (key-actuated) switches like the DX-D2/D3 and the DX-W lock family use a metal key on the door entering the switch head. Strengths: positive mechanical engagement, forced contact separation, and — on locking types — the holding function itself. Weaknesses: they demand door alignment within about a millimeter, wear with traffic, and collect debris in the key slot.
Non-contact switches remove the mechanical coupling entirely. The DAIDISIKE DX-C1 coded-magnet switch senses up to 17 mm in both the Z and Y directions, tolerating sagging hinges and rattling doors; it is rated IP65 as standard with IP67/IP68 available. The DX-R1 non-contact switch gives an assured switch-on distance of 0–10 mm and assured switch-off above 25 mm, with dual-channel solid-state outputs (150 mA) plus a 50 mA auxiliary output, a 60 ms response time, and IP65 protection.
Choose non-contact for doors that see misalignment, vibration, frequent washdown, or very high cycle counts; choose contact-type when you need guard locking or maximum resistance to brute-force opening — or combine them: non-contact sensing on light doors, locking switches on walk-in cells.
Step 4: What Coding Level Do You Need Against Defeat (ISO 14119)?
Interlocks fail in practice mostly by being defeated: a spare key taped into the switch, a magnet held against a reed sensor. ISO 14119 addresses this with coded actuators — the switch only responds to its matching actuator — in low-coded and high-coded grades.
The DX-C1 is a coded-magnet switch: multiple magnetically sensitive elements must trigger in a defined sequence, so a simple magnet from the toolbox will not actuate it the way it would a plain reed sensor. The DX-R1 goes further with explicitly selectable coding per ISO 14119: universal-coded (S) versions accept any DX-R1 actuator, while unique-coded (D) versions pair to one specific actuator — the anti-defeat choice where operators have motive and opportunity to bypass the guard. The DX-D6 likewise offers S or D coding in its ordering matrix.
Assess defeat incentive honestly: if opening the door mid-cycle would save an operator significant time, specify high coding and mount switches out of easy reach. Note also that the DX-D6 uses its own RFID-coded key system (DX-K9S/DX-K9D), separate from the mechanical DX-K1–K8 keys.
Step 5: Contacts, Outputs, and Wiring Into the Safety Circuit
For contact-type switches, pick the NC/NO complement to match your safety relay and any auxiliary signaling. The DX-D2/D3 range offers four configurations (1NC+1NO, 2NC, 2NC+1NO, 3NC); the DX-W2 offers 14 contact configurations across two independent contact compartments — 28 catalog models across the two locking types — letting one compartment monitor the door and the other monitor the lock. The DX-W5 provides six gold-plated silver-alloy contact blocks in four configurations, with contact ratings including AC-15 240 V/3 A and a DC-13 250 V/2.7 A tier.
For electronic non-contact switches, match output type to the controller: the DX-R1 comes in NPN and PNP versions, in 4-wire (F-type) or 6-wire cascade (E-type) wiring. Cascading matters on multi-door cells: E-type DX-R1 switches, DX-C1 switches, and DX-D6 switches can all be wired in series so several guard doors are monitored through a single safety relay input.
Whatever the switch, the safety evaluation belongs in a monitored device — a safety relay such as the DAIDISIKE DQSRN or DA31 — which checks both channels, detects shorts and welded contacts, and switches the machine contactors with feedback monitoring.
Step 6: Keys, Actuators, and Mechanical Installation
Actuator selection is where door-switch projects most often stumble on site. DAIDISIKE's DX-K operation key series (11 models, DX-K1 through DX-K8 with variants) fits the DX-W2, DX-W3, DX-W5, DX-D2, and DX-D3 switch bodies, with a specified key-to-slot insertion tolerance of ±1 mm.
Match the key to the door movement: sliding doors can use rigid straight keys, while hinged doors need either an angled-entry key or an adjustable one — the DX-K5 adjusts horizontally, the DX-K6 horizontally and vertically, and the DX-K8 adds a press-3 mm, rotate-90° operating head for awkward geometries. Hinged (swing) door installations require a minimum swing radius of R > 300 mm; tighter radii bind the key in the slot and wear the head.
Leave preparation clearance before fitting — 1–3.5 mm for the DX-W2/W3/W5 family, 1–2.5 mm for DX-D2/D3 — and on full-body-access doors, prefer the DXL bolt assembly: the operator gets a proper handle, the switch gets a guided, repeatable key entry, and the door gap tolerance (1–10 mm) absorbs fence-panel reality.