The 8-character limit sits on the panel's own device name field in the Ethernet setup. That name is a label inside the panel project and never has to match a controller name past 20 characters. Give the panel a label of 8 characters or fewer, leave the controller name alone, and put the controller's address in the connection fields.
The field that stopped you is the device name field in the panel manager's Ethernet setup, and its 8-character limit applies to the panel's own label for the device. The controller name, which runs past 20 characters, lives in the controller's programming project. The two names never have to match. The panel reaches the controller through the driver you select and the address you enter in the connection setup, so the fix is small: type a short label into the device field, leave the controller name alone, and spend your attention on the connection. This page separates the three fields, lists the character counts you will meet, and works one case end to end.
What the device name field actually is
The device name is the label the panel project uses for one device entry. Your tags point at that entry by this label, and the entry carries the driver and the address that do the communicating. The field sits in the Ethernet setup of the panel manager, and in the case at hand it accepted 8 characters.
The controller name is a different object in a different program. It is the identity the controller carries in its own programming project, and the controller software accepted a name past 20 characters. Nothing you type on the panel changes it.
That is the whole distinction. One field is a label for your project. The other is the controller's identity. The connection is built from a third thing entirely: the driver and the address.
Where each name lives
| Field | What it is | Where it is set | Length in the case at hand |
|---|---|---|---|
| Controller name | The controller's identity in its programming project | The controller programming software | Past 20 characters |
| Device name | The panel project's label for one device entry | The panel manager, Ethernet setup | 8 characters |
| Connection target | The address or path the panel's reads and writes follow | The connection setup for that device | An address from your network plan |
Three fields, three jobs. Only the device name rejected your entry, and it rejected it for length, not for content.
Character limits belong to single fields
Every limit you meet is a property of one field:
- 8 characters, the device name field in the panel manager's Ethernet setup, in the case at hand.
- 128 characters, the scroll text object in one documented panel line, for text placed on a screen.
- 30 alphanumeric characters, one automation team's documented naming convention for new devices.
- 254 characters, the length a network host name can reach.
Plan each permanent label to the shortest field on its route. In this panel project that field is the 8-character device name, so the working habit is an 8-character label, and the controller's long name stays where it already fits.
Example: a 21-character controller name against an 8-character field
The inputs:
- Controller name: 21 characters. The case has a name past 20 characters, and 21 is the shortest length that satisfies it.
- Device name field: 8 characters, the limit shown in the panel manager's Ethernet setup in the same case.
- Scroll text object: 128 characters, the documented limit for on-screen text in one panel line.
The rule in words: a label fits a field when its length is less than or equal to the field's limit, and the panel reads the controller through the driver and the address fields whatever the two names say.
The arithmetic:
- 21 - 8 = 13. The controller name is 13 characters longer than the device field accepts, so no panel-side edit will ever hold it whole.
- Build to the field: L, I, N, E, 2, C, P, U is 8 characters. 8 is at the limit, so the field accepts LINE2CPU.
- If the full name must reach the screen, the text object takes it: 21 is below 128, with 107 characters to spare.
The result: the device entry is labeled LINE2CPU, the controller keeps its 21-character name, the controller address goes in the connection setup, and the tags point at the device by its label.
The decision: 8 characters or fewer and the field accepts the entry; above 8 it rejects it. The words inside the 8 are yours. If the panel accepts the label and still shows no data, stop editing names, because the fault has moved past the label into the connection.
How the panel actually reaches the controller
Three things carry the data:
- The driver selected for the device entry. It has to match the controller's communication interface; matching an HMI driver to the PLC Ethernet interface covers that choice on a shared switch.
- The address or path in the connection setup, taken from the network plan for that controller.
- The tag addresses, which point at the device entry by its label; setting the tag device and PLC address without guessing walks that step.
The panel manager is also where the controller type is declared; setting the PLC type in the panel manager shows that screen. On a serial link the same order holds, and checking the PLC protocol before replacing a legacy HMI panel is the matching first move.
Test with one known value from the controller. If it updates on the panel, the setup is finished. If it does not, work the list in order: driver, address, network, tags.
One safety note: leave the controller name as it is, because renaming a controller means downloading a project to it, and a download to a controller running the machine belongs in a planned stop.
When the name has to show on the screen
Operators know the line by what the screen shows, so the long name belongs on the display, and the short label in the device field. On-screen text carries far more: the documented scroll text object allows 128 characters, which holds the 21-character name six times over.
Plan letters at 30 ft of viewing distance per inch of capital height, the standard signage planning figure (FHWA), and use 20 ft per inch where the reader must catch the word at a glance; keep line spacing at 1.7 x the capital height. A panel read from 6 ft needs capitals of 6 / 30 = 0.2 in at the planning figure, or 6 / 20 = 0.3 in for glance reading. LINE2CPU at 0.3 in capitals reads in one glance from that distance.
If the area also needs a notice board that plays pictures and video from a memory card, with no controller involved, that is a separate screen for shop-floor signage displays.
What to do
Recommendation: When the device name field rejects the controller name for length, give the panel its own label of 8 characters or fewer, leave the controller name unchanged in its programming project, and enter the controller's address in the connection setup. Apply this whenever the field you are fighting is the panel's label field. If the field you are fighting is on the controller side, set the name there instead and let the panel keep its short label.
Write the label into your electrical documentation next to the controller address. The next person to open the panel project looks for the device by that label, and the name on the controller still tells them what it is.
Questions
Does the HMI device name have to match the PLC controller name?
No. The device name is the panel project's label for the device entry, and the controller name is the identity in the controller's programming project. The panel connects through the driver and the address fields, so the names never have to be equal. Keep labels unique within one panel project, because tags point at the device by that label; two separate projects can use the same label without conflict.
What do I type in the device name field when the controller name is too long?
A label of 8 characters or fewer, built from what identifies the machine to you: a line number, an area, a unit type. For example LINE2CPU, eight characters exactly. Only the length is fixed by the field; the characters themselves are your choice, and they carry no meaning to the connection.
The panel accepts the label but shows no data. What do I check?
Work the connection in order: the driver selected for the device, the controller address or path, network reachability from the panel, then the tag addresses. Make one known controller value your test case, and transfer the project once after the checks so you make a single download instead of several.
Can the full controller name appear on the panel screen?
Yes. Screen text fields carry far more than the device field; one documented scroll text object allows 128 characters, which holds a 21-character name six times over. Keep the long name on the display for the people who read it, and the short label in the device field for the project that references it.
Should I shorten the controller name instead?
No. The name past 20 characters is valid where it lives, in the controller's programming project. Shortening it buys nothing on the panel side and costs a project download to the controller, which belongs in a planned stop on a running machine. Touch it only for a reason from your own naming standard, and record the change with the controller documentation.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.