Configuring Local Mode Operation and Interlock Bypassing in CEMAT and APL

To operate a motor in local mode from field pushbuttons without tripping on software interlocks in SIMATIC PCS 7, configure the drive block's native local operating mode and protection bypass attributes rather than manually forcing interlock inputs. In PCS 7 CEMAT (C_DRV_1D), set the local operating mode parameter L_OPMOD to authorize local start/stop while evaluating or neglecting electrical and protection interlocks (EBVG, ESVG) according to plant safety requirements. In the PCS 7 Advanced Process Library (APL MotL), set LocalSetting = 2 (or 4) and set parameter BypProt = 1, which automatically bypasses interlocks in local mode and simulation while maintaining safety integrity.

Local Mode Architecture in Industrial Motor Control

In heavy process industries (such as cement, mining, and bulk material handling), motors and conveyor drives require local control capabilities near the physical equipment for maintenance, commissioning, and emergency operations. When a field technician operates a local control station (pushbutton box with start, stop, and local/remote selector), the automation system must transition the drive into local mode.

A frequent operational dilemma arises regarding safety and process interlocks: should a local motor run even if upstream process interlocks (such as bin level limits or chute blockages) are active? Both the specialized PCS 7 CEMAT library and the standard Advanced Process Library (APL) provide pre-engineered parameters to manage interlock behavior in local mode without requiring technicians to manually bypass logic blocks in the DCS.

CEMAT C_DRV_1D vs APL MotL Local Mode Mechanisms

The two major PCS 7 library architectures handle local mode via specific technological interfaces:

CEMAT Drive Architecture (C_DRV_1D / C_DRV_2D):
- Evaluates dedicated binary interlock inputs: EBVG (Electrical Interlock / Schutzschalter), ESVG (Process Interlock / Betriebsverriegelung), and EVVO (Start Interlock).
- Operating mode is selected via L_OPMOD (Local Operating Mode): mode 1 (local via field switch), mode 2 (local via DCS selection), or mode 3 (test mode). In local mode, parameterization determines whether EBVG and ESVG must be satisfied or bypassed.
APL Motor Architecture (MotL / MotRevL):
- Configured via LocalSetting (integer values 1 to 5):
- LocalSetting = 1: Control via faceplate only.
- LocalSetting = 2: Control via local field signals; faceplate tracks motor state.
- LocalSetting = 4: Control via local field signals; motor runs without interlocks.
- Parameter BypProt (BOOL): Setting BypProt = 1 explicitly enables bypassing of protection interlocks (Protect) while in Local Mode and Simulation Mode.

Local Operating Modes and Interlock Bypass Comparison

The table below details parameterization differences between CEMAT and APL for local motor operation and interlock handling.

Library SystemBlock TypeKey Mode ParameterInterlock Bypass ParameterOperational Behavior in Local ModeCEMAT MineralsC_DRV_1DL_OPMOD = 1AUT_ON = 0 / Local Mode FlagRuns via local pushbuttons; evaluates EBVG; can neglect process interlocksCEMAT MineralsC_DRV_1DL_OPMOD = 2Operator Local SelectMotor operated locally after DCS operator issues local release commandPCS 7 APLMotLLocalSetting = 2BypProt = 0Local pushbuttons control motor; interlocks (Intlock, Protect) remain fully activePCS 7 APLMotLLocalSetting = 2BypProt = 1Local pushbuttons control motor; protection interlock (Protect) is bypassedPCS 7 APLMotLLocalSetting = 4Built-in BypassLocal mode runs without interlocks; faceplate displays local bypass indicator

Step-by-Step Procedure to Configure Local Mode Operation

Follow this procedure in CFC to configure safe local mode operation without manual logic forcing:

Configure APL MotL for Local Mode with Interlock Bypass:
- In the CFC chart containing MotL, set parameter LocalSetting = 2.
- Interconnect local field digital inputs: connect Local/Remote switch to LocalLi, Start pushbutton to FwdLocal, and Stop pushbutton to StopLocal.
- If plant operating philosophy permits bypassing protection during maintenance, set parameter BypProt = 1.
Configure CEMAT C_DRV_1D for Local Operation:
- In the CFC editor, open C_DRV_1D block properties.
- Assign L_OPMOD according to the field wiring philosophy (typically Mode 1 for hardwired local switches).
- Wire the local start signal to ESTV (Local Start Pushbutton) and local stop to ESTP.
- Review plant electrical safety rules: ensure hardwired Emergency Stop pushbuttons actuate the main contactor directly and remain unbypassed in software.
Compile and Download:
- Compile CFC changes using delta download mode and transfer to the automation system.

Verification

Verify local mode functionality through the following field commissioning tests:
1. Switch the local selector switch to 'Local': verify that MotL.LocalAct = 1 (or CEMAT LOCAL = 1) appears on the faceplate.
2. With process interlocks simulated inactive (Intlock = 0): verify that pressing the field Start pushbutton starts the motor when BypProt = 1.
3. Depress the field Stop pushbutton: verify that the motor immediately de-energizes (FwdAut = 0).
4. On the WinCC faceplate, verify that the local operating symbol and bypass indicator (if applicable) are clearly displayed to the operator.

Limitations and Operational Precautions

Never bypass hardware electrical safety circuits (such as emergency pull-cords, thermal overload relays, or safety gate limit switches) through software parameters like BypProt. Software interlock bypassing is intended strictly for process interlocks during controlled maintenance. Physical safety devices must remain hardwired directly into the drive breaker control circuit to guarantee personnel and equipment protection under all operating conditions.

Engineer FAQ

What is the difference between LocalSetting 2 and LocalSetting 4 in APL?

In LocalSetting 2, interlocks are evaluated unless BypProt is explicitly enabled. In LocalSetting 4, the motor runs locally without evaluating any interlocks natively, intended for critical maintenance drives.

Can the DCS operator force a motor out of local mode from WinCC?

If local mode is initiated by a physical field switch wired to LocalLi, field control takes precedence. The DCS operator cannot override local mode until the field switch is returned to Remote.

Does CEMAT generate an alarm when a drive is switched to local mode?

Yes. CEMAT logs operating mode changes in the WinCC alarm system to ensure that plant operators are aware that equipment has been decoupled from automatic sequence control.