Sigma Control 2
Sigma Control 2 replaced the original Sigma Control on units built roughly post-2011. Configuration & event history are portable via SD card, which makes controller swaps straightforward when a board fails. Do not power the unit up with the SD card missing on units configured to require it.
Manufacturer
Kaeser
Display
2-line 20-character alphanumeric backlit LCD (STN), 4 discrete status LEDs (Power, Running, Communication, Alarm), 12-key membrane keypad with soft menu keys.
Years produced
~2011 – present (replaced original Sigma Control which shipped 1998–2011).
Power supply
24 VDC internal, fed by 100–240 VAC control transformer (unit dependent). Battery-backed real-time clock (CR2032).
Ambient range
0 – 46 °C ambient inside the cabinet (typical). Derate above 40 °C.
Protection rating
IP54 front / IP20 rear when installed in the OEM cabinet.
Relay outputs
Up to 8 configurable digital outputs (star/delta/main, blowdown solenoid, dryer, alarm, load, common trouble).
Replaces
Sigma Control (original / mono LCD)
Used on
- Kaeser SK / SM / SX series
- Kaeser ASD / BSD / CSD / DSD / ESD / FSD series
- Kaeser HSD tandem units
- SFC variable-speed units (paired with SFC drive)
- Retrofit on many older Kaeser SM units
On AirCompDX
Features
- Dual-mode Sigma Control logic (Dual, Quadro, Vario, Continuous, Dynamic, Automatic)
- Real-time clock with weekly timer & holiday schedule (up to 4 pressure bands / day)
- Trend logging to SD card (up to weeks of 1-min samples)
- Modbus TCP / RTU / Profibus / Profinet (module dependent)
- Sigma Air Manager 4.0 native integration
- Password-protected service and factory menus
- Motor start counter, hour meter, load hour meter, event log with timestamp
Interfaces
- SD card slot (firmware, event log, parameter backup/restore)
- Ethernet RJ45 (Sigma Network, Modbus TCP, optional Profinet)
- RS-485 (Sigma Control Basic, Modbus RTU, Profibus DP with plug-in module)
- Digital I/O for remote start/stop, load/unload, common alarm, dryer control
- Optional bus modules: Profinet, EtherNet/IP, DeviceNet
Sensor inputs
- T1 airend inlet temp (PT1000)
- T5 airend discharge temp (PT1000)
- T6 aftercooler outlet temp (PT1000)
- P1 line/network pressure (4–20 mA)
- P2 sump / internal pressure (4–20 mA)
- dP oil-separator differential (4–20 mA option)
- dP air-filter differential (4–20 mA option)
Common fault codes
First checks
- Reset overload relay in starter cabinet
- Check FLA vs nameplate, look for phase loss or voltage imbalance
- Verify no seized airend / high oil temp shutdown just prior
- Check motor PTC continuity if fitted
First checks
- Check oil level and cooler cleanliness
- Verify thermostatic valve opening between 71–85 °C
- Confirm ambient / cabinet airflow
- Test T5 PT1000 (~1385 Ω @ 100 °C)
First checks
- Release local E-stop
- Check remote E-stop loop / jumper on X2
- Confirm 24 VDC on safety input
First checks
- Verify all three phases at disconnect
- Confirm airend rotation direction (arrow on drive)
- Check phase-sequence / phase-loss monitor relay
Oil separator ΔP highDifferential across separator element above alarm (typ. > 1 bar / 15 psid at full load).
First checks
- Replace separator element and oil filter as a set
- Change oil if past interval
- Check for foaming or wrong oil type
- Verify scavenge line & orifice clear
First checks
- Reseat SD card / bus module
- Check RS-485 or Ethernet cable and 120 Ω termination
- Cycle 24 VDC control power
First checks
- Verify cabinet heater operation
- Confirm ambient
- Check T1 sensor and wiring
First checks
- Read drive keypad for specific F-code
- Check drive cabinet cooling filter
- Verify DC bus discharge before opening
First checks
- Test drain manually
- Check drain 24 VDC and level probe
- Clear strainer / Y-filter upstream
Service due (Air filter / Oil filter / Separator / Oil / Motor)One of the service hour counters at 0.
First checks
- Perform the specific service
- Reset that counter (only) in service menu
- Verify service interval is set per fluid choice (S-460 vs SR)
First checks
- Replace CR2032 battery on control board
- Re-set date/time & weekly timer
First checks
- Check sensor wiring polarity
- Test sensor with known reference
- Look for water in sensor cavity
Fault list is non-exhaustive and firmware-dependent. Always confirm against the controller’s on-screen help or OEM manual.
Wiring notes
- 24 VDC control voltage supplied by internal PSU from 120/230 VAC control transformer
- Digital inputs are 24 VDC sinking, isolated from mains
- Motor contactor coils driven by relay outputs (24 VDC or 120/230 VAC per package)
- VFD comms via Modbus RTU (SFC drives) — verify baud & address match
- Sensor cabling shielded, ground shield ONE end only at controller
Terminal & connector map
Pinouts distilled from OEM wiring diagrams. Exact silk-screen labels and pin numbering vary by hardware revision and package options — always confirm against the machine’s as-built wiring diagram before landing a wire.
Connectors to the controller
- X1 – 24 VDC control power in from unit transformer (top-left screw terminals)
- X2 – RS-485 SIGMA NETWORK, 3-pin plug-in (A / B / SHIELD) — daisy-chain to SAM master, termination resistor at last node
- X3 – RJ45 Ethernet port (SIGMA CONTROL 2 module, right side) — SAM 4.0 / SmartAir uplink
- X4/X5 – analog sensor plug-in headers (PT1000 + 4–20 mA), keyed by color
- X6 – SD card slot behind the door (configuration & event log); never remove with power on
- X10 – digital I/O to starter panel (star/delta contactors, blowdown solenoid, remote start/stop, common trouble)
X1Control power
| Pin | Signal | Type | Connects to |
|---|---|---|---|
| L+ | +24 VDC in | 24 VDC | Unit control transformer + |
| L− | 0 V / GND | 24 VDC ret. | Unit control transformer 0 V |
| PE | Protective earth | PE | Cabinet ground bar |
Fused ahead of the terminal per unit schematic (typ. 2 A slow).
X4 – TemperaturePT1000 airend / cooler sensors
| Pin | Signal | Type | Connects to |
|---|---|---|---|
| 1 / 2 | T1 airend inlet | PT1000 | T1 sensor at inlet housing |
| 3 / 4 | T5 airend discharge | PT1000 | T5 sensor at airend outlet |
| 5 / 6 | T6 aftercooler out | PT1000 | T6 sensor at aftercooler |
3-wire wiring recommended on runs > 5 m; two-wire OK for factory-fitted sensors.
X5 – Pressure4–20 mA transducers
| Pin | Signal | Type | Connects to |
|---|---|---|---|
| P1+ | P1 network pressure loop + | 4–20 mA | P1 line transducer |
| P1− | P1 loop return | 4–20 mA | P1 line transducer |
| P2+ | P2 sump pressure loop + | 4–20 mA | P2 sump transducer |
| P2− | P2 loop return | 4–20 mA | P2 sump transducer |
| dP+/− | Separator ΔP (option) | 4–20 mA | Sep ΔP transducer |
X10 – Digital I/OStarter panel & remote
| Pin | Signal | Type | Connects to |
|---|---|---|---|
| K1 | Main contactor coil | 24 VDC out | K1 main contactor |
| K2 | Star contactor coil | 24 VDC out | K2 star contactor |
| K3 | Delta contactor coil | 24 VDC out | K3 delta contactor |
| Y1 | Blowdown / venting solenoid | 24 VDC out | Y1 blowdown solenoid |
| RS | Remote start (dry contact in) | dry contact | Customer PLC / BMS |
| RSt | Remote stop (dry contact in) | dry contact | Customer PLC / BMS |
| AL | Common trouble output | relay out | Master alarm / BMS |
Do not mix 24 VDC I/O and 120 VAC on the same terminal bank.
Known issues & field notes
- SD card write errors: use industrial-grade SD, keep <16 GB, FAT32; do not hot-swap while running
- RTC drift on units powered off long-term — swap CR2032 at every major service
- Ethernet port sensitive to plant surges — use surge-protected patch panel
- P2 sump pressure sensor moisture ingress in humid installs — mount transducer upright
Retrofit notes
Original-Sigma-Control-to-SC2 retrofit is a dealer-supported kit for many SM / SK / BSD frames. Wiring loom and separator ΔP transducer usually need to be added.
Firmware notes
Multiple firmware families exist for compressor / booster / vacuum builds — do NOT cross-flash. Keep a known-good SD image before any update.
Service menu is PIN-protected; site owner sets via Kaeser dealer — do not brute-force. Factory menu is dealer-only.
Field reference
Condensed working reference. Cross-check against the OEM service manual before torqueing anything.
First-start / commissioning
- Verify T1 secondary is 24 VDC ±10% at X1 before energizing SC2
- Confirm SD card is seated and formatted for the correct unit (SC2 will refuse to run without it if configured)
- Set line pressure setpoint 10 psi below relief valve; deadband ≥ 8 psi to avoid short-cycling
- Rotate motor by hand and jog for correct rotation BEFORE clearing 'phase failure' alarm on first energize
- Let unit run 15 min unloaded; verify T5 climbs and stabilizes before loading
Torque specs
- PT1000 sensor into airend port
- 20–25 Nm (15–18 ft-lb)
- 4–20 mA transducer 1/4" NPT
- 15–20 Nm (11–15 ft-lb)
- X1 / X10 screw terminals
- 0.5–0.6 Nm (4.5–5.5 lb-in)
- Ethernet / SIGMA NETWORK plug
- hand-tight (do not use tool)
Jumpers & DIP switches
- J1 – Modbus RTU termination (last node)
- ON at end of RS-485 chain, OFF elsewhere
- J2 – 24 VDC / dry-contact remote start
- 24 VDC = jumper INSTALLED; dry contact = jumper REMOVED
- SW3 – SIGMA NETWORK station address
- DIP set per site network map (never duplicate)
PM intervals
- 500 h / 6 moCheck event log; export via SD card; verify sensor readings vs mechanical gauges
- 3,000 h / annualReplace CR2032 RTC backup battery; verify network sync time
- 8,000 hInspect connector strain reliefs; retorque terminal screws; blow dust from HMI vents
Field tips
- 'Emergency stop' with no button pressed → check X10 E-stop loop wiring first, not the button itself
- Random comm dropouts on Sigma Network → almost always cable routing next to VFD or unshielded ground
- SD card write errors after 5+ yr → replace with Kaeser OEM industrial-grade card; consumer SD cards fail
Manuals & literature
Kaeser — support portal
Manuals gated — request via local rep or parts portal
Your manuals
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