Manual Command Protection

Manual Mode does not bypass the installation’s safety systems or equipment protections. Every requested action remains subject to the conditions required for its permitted operation.

A manual command requests an equipment action. The control program determines what outputs and supporting functions are required to carry out the request and evaluates the permissives, interlocks, and conflict checks affecting them before executing the action.

A safety system prevents or limits an action independently of the control program. Manual Mode cannot override, defeat, or replace that function. When the safety system prevents the requested action, the control program cannot authorize it.

For example, if opening a guarded access door causes the safety system to remove torque from a servo drive, the safety system prevents the drive from producing torque regardless of any command from the control program. In a PLC Pro installation, the control program also monitors drive availability and does not issue the Manual Mode jog command while the drive is unavailable.

Similarly, if a safety function removes pneumatic pressure through a safety-rated dump valve, the control program does not execute a requested Manual Mode action that requires pneumatic motion. The safety system independently prevents the actuator from receiving the energy required to move, while the control program also inhibits the requested action because pneumatic operation is unavailable.

Within the control program, equipment protections are implemented through the permissives, interlocks, and conflict checks applied to the outputs and supporting functions required for an action. These protections prevent operation that could damage equipment, tooling, product, or process, and remain effective in Manual Mode.

A typical permissive would be a minimum liquid level required for a pump. If the detected level is too low, the control program does not issue the pump command in Manual Mode, preventing operation that could damage the pump by running it dry. Proper liquid level is therefore a permissive for engaging the pump output.

A motor overload may be interlocked with the motor control circuit. During troubleshooting, the operator may deliberately command the motor to run in Manual Mode. If the control program issues the command but the motor does not respond, maintenance can then determine whether the overload is tripped, a wiring problem exists, or another field condition is preventing the motor from running.

Consider a conflict check for a motor controlled by separate “FORWARD” and “REVERSE” contactors. Either direction may be requested in Manual Mode, but energizing both contactors at the same time could damage the motor-control equipment. The conflict check therefore prevents either output from being commanded while the opposing output is active.

A command issued in Manual Mode requests an equipment action. The operator command is received by the control program as an input; it does not directly operate the outputs that perform the action. The control program determines if and how the requested equipment action is carried out.

Each command issued in Manual Mode is linked in the control program to the equipment action it requests and to the outputs required to carry out that action. A single equipment action request may require one output or the coordinated operation of several outputs.

For example, a command to jog a conveyor in reverse may require the control program to provide a speed reference, select the reverse direction, and then issue the run command to the drive. One equipment action request therefore results in several output commands required to carry it out.

A requested action may also require supporting functions that are not themselves the object of the operator’s request. Those supporting functions are linked in the control program to the requested equipment action and are operated as required to carry it out.

For example, jogging a mechanism driven by a motor with a spring-applied brake may require the control program to release the brake before commanding the motor to run. The operator requests movement of the mechanism, not release of the brake. Brake release is a supporting function linked to the requested equipment action and operated as required to carry it out.

The PLC Pro evaluates the permissives, interlocks, and conflict checks affecting each required output and supporting function. When any of those conditions prevents a required output or supporting function from being used, the control program does not issue the command that depends on it and HMI identifies the condition preventing the requested action.

When the required outputs and supporting functions are available for use, the control program executes the requested equipment action. The operator’s request is thereby translated into the output commands required to perform the action.

• Manual Mode does not bypass the installation’s safety systems or equipment protections.
• A manual command requests an equipment action; it does not directly operate the outputs that perform the action.
• Each manual command is linked in the control program to the outputs needed to carry it out.
• The PLC Pro applies the required permissives, interlocks, and conflict checks to each manual command.
• The PLC Pro ensures that HMI identifies why a requested action cannot be carried out.
• When the required outputs and supporting functions are available for use, the control program executes the requested equipment action.