Password protect an HMI setpoint screen at entry

What you need

• The HMI project file and the editor that opens it, on the engineering workstation.
• A map of the routes into the setpoint screen: screen-change pushbuttons, a screen selector, and screen changes the PLC commands.
• A password for each screen you will lock, chosen to your site's rules; a 4-digit numeric password is the common form on these panels. Keep a note of who receives it.
• Your site's change procedure for sending an updated project to the panel, because the password travels with the project.

This procedure locks entry to a setpoint page. The panel's engineering setup menu is a separate guard with its own key path; password protect the HMI setup menu key path covers that lock.

Find every route into the setpoint screen

Open the project and list every object and function that can bring the panel to the setpoint screen. This editor has three kinds of route into a screen:

• A screen-change pushbutton on any screen, targeted at the setpoint page.
• A screen selector, the list object an operator picks a destination screen from.
• A screen change the PLC commands, where the controller tells the panel which screen to open.

Walk through each screen in the project, note each route, and write down the screen it targets. If a route lands on a different screen that also holds editable setpoints, add that screen to the list; it gets its own password. Keep the route count from this pass. The test before startup works through it one route at a time.

Set the password on the destination screen

1. Open the setpoint screen in the editor.
2. Open the screen's option settings: from the top menu, Screen > Screen Option, or right-click the screen in the screen navigator on the left and choose Screen Option.
3. Open the Password tab and assign the password for this screen.
4. Repeat for every other screen on your list that holds editable setpoints.
5. Save and send the project to the panel through your site's change procedure. Passwords are stored in the project, so the panel asks for the new one only after the transfer.

Why the button password leaves routes open

A password on the pushbutton guards that pushbutton alone. The objects on the page split too: numeric-entry controls can carry passwords, and buttons that set an ON or OFF state, or toggle a value, cannot carry passwords at all. Object-level protection on a setpoint page therefore means a password on every numeric entry, none on the ON/OFF objects, and a page that any open route still reaches. The setting on the destination screen closes all of that with one assignment: it gates the page itself, it gates every route into the page, and it needs no password on the objects.

Worked example: three routes into one setpoint screen

Inputs, from the editor's documented behavior and the project's own layout:

• 3 routes into the setpoint screen, one of each kind: the Setpoints pushbutton on the main menu, the screen selector, and the PLC-commanded screen change.
• 1 destination screen holding 2 editable numeric entries and 1 ON/OFF button.
• 1 screen password of 4 digits, assigned on the screen's option settings.
• The documented rules: the password on the screen's option settings is checked on entry by any method; numeric-entry controls can carry passwords; ON/OFF and toggle buttons cannot.

Rule in words: a password on a route guards that route. A password on the screen guards the screen, so the routes it covers equal the routes that exist.

Arithmetic:

• Pushbutton password only: 1 of the 3 routes guarded, so 3 - 1 = 2 routes stay open.
• Object passwords only: 1 password per numeric entry, 0 possible on the ON/OFF button, 0 of the 3 routes gated.
• Screen setting: 1 assignment, 3 of 3 routes gated, every object on the page behind it.

Test load: each route tried once with the correct password and once with a wrong one gives 3 × 2 = 6 entries per pass; on the bench that pass takes about 15 minutes for a panel with 3 routes.

Result: 1 assignment on the screen replaces 1 button password plus 2 object passwords, and it closes the 2 routes the pushbutton password leaves open. The decision threshold is the route count: when a setpoint screen can be reached by more than 1 route, put the password on the screen. With exactly 1 route, a pushbutton password works, and the screen setting still covers the objects in the same single step.

Recommendation: Set the password on the destination screen's option settings whenever a setpoint screen can be reached by more than one route, assign a password to every screen that holds editable setpoints, and test each route with a correct entry and a wrong entry before the panel goes back on the machine.

Check every route before the panel goes back to work

1. Press the screen-change pushbutton: the password prompt appears before the setpoint page shows.
2. Pick the setpoint screen from the screen selector: the prompt appears here too.
3. Fire the PLC-commanded screen change on the bench, or in a window when the line is down, and watch the panel: the prompt appears. Budget 15 minutes for the full pass on a screen with 3 routes.
4. Enter the correct password once per route and the page opens. Enter a wrong password once per route and the setpoint page stays closed.
5. Open each other screen that holds editable setpoints and check that its own prompt appears.
6. Repeat the pass after any later change to the project's navigation. A new route is gated by the screen setting, and the pass also catches a new object aimed at a setpoint screen with no password.

Keep the range limits in the PLC as well

The screen password decides who opens the page. It says nothing about the values an authorized user types: an operator cleared to enter the page could still type 500 °C into a setpoint whose safe range is 0 to 120 °C. So the allowed range for each setpoint belongs in the control logic too, where it holds even for an authorized edit. Put the low and high checks where the value is edited, and keep a range check in the controller as the second guard; validate high and low HMI setpoints before they reach the PLC shows the pattern for the pair.

Questions