The PLC value for the 4–20 mA output starts in binary, while the C-more Micro numeric and meter displays are being fed BCD data; the tenths fail when the value conversion, scaling, and display format do not agree. Keep the output command separate from its display representation, then verify each conversion boundary.
Keep the 4–20 mA output value separate from display formatting
A value in a PLC V-memory location may be a raw module command, a scaled engineering value, or a value prepared for display. Those are not interchangeable. Converting a binary value to a real number in a PLC data view does not prove that the HMI object accepts a real value; the numeric display and meter in this setup were being used with BCD data.
Do not change the output value just to make the HMI look right. If that V-memory location directly drives the analog output module, changing its scale can change the commanded output. Use a separate display value or a controlled conversion path, and retain the existing output value until the relationship is known.
- Identify the V-memory address used by the output module.
- Identify the value address each HMI object reads.
- Determine whether each address contains binary, BCD, or a scaled engineering value.
Check: Monitor the output command and the HMI source values online. Confirm which one changes when the display conversion logic runs before editing the output path.
Trace the value through binary, scaling, and BCD
BCD represents decimal digits; it does not by itself preserve an implied decimal point. A BCD value representing 123 contains the digits 1, 2, and 3. A separate scale convention or display format must make that value mean 12.3 rather than 123. If the PLC scales the value incorrectly before or during BCD conversion, the HMI can show a whole number or the wrong magnitude even though the digits appear valid.
Trace the value in order: source binary value, engineering scaling, integer value used for tenths, BCD conversion, then HMI object. Do the arithmetic in the PLC's intended numeric representation before encoding the result as BCD. Do not treat packed BCD bits as an ordinary binary integer unless the PLC instruction set specifically supports that operation.
| Observed symptom | Likely check |
|---|---|
| Whole numbers display correctly, but tenths do not | Check whether the numeric object is configured to show one fractional digit and whether the source value carries the corresponding implied scale. |
| The value is correct in a PLC data view but not on the HMI | Check the HMI object's accepted data format and the conversion into its source address; a real-valued view does not establish that the HMI object reads REAL data. |
| The value has the wrong magnitude or digit pattern | Check BCD conversion and the scaling instructions in sequence, including the value immediately before and after each operation. |
Check: Compare the online source, scaled integer, and BCD result. Each stage must represent the same intended quantity under its own format before you configure the display.
Represent tenths as a scaled integer
Use an integer scale that preserves one decimal place, then make the display place the decimal point. For a desired value of 12.3, the corresponding integer tenths value is 123. This is an illustrative representation, not an output-module range or a prescribed PLC instruction. Apply the scale appropriate to the actual source and units.
Keep one documented convention throughout the display path. For example, if the PLC prepares an integer whose units are tenths, the HMI numeric object must show one fractional digit. If the PLC instead supplies whole engineering units, applying the same fractional-digit format would misrepresent the magnitude. Do not scale twice—once in PLC logic and again in the HMI.
- Write down the source units and what one count represents.
- Calculate the integer value that represents the desired tenths precision.
- Convert that scaled value to the format the HMI object actually reads.
- Keep this display value separate if the output module uses a different raw range or scale.
Check: Test a known value with a fractional part and confirm the scaled integer and its intended engineering value agree before enabling the display update.
Correct the BCD scaling path before converting
The reported correction involved both configuring one fractional digit and correcting BCD-related scaling instructions. A display-format change alone cannot repair a wrongly scaled PLC value. Conversely, correct PLC scaling can still look like a whole number if the numeric object shows no fractional digit.
Review each instruction that changes the value. Confirm the source and destination formats, the scale operation, and whether conversion occurs before or after the scale. Use the PLC's documented instruction behavior for binary-to-BCD conversion; do not substitute a real-number conversion if the HMI object reads BCD. No specific instruction, factor, or range can be selected without the PLC model and the existing logic.
As a temporary production restore, return to the known-working whole-number display or use a separately verified display value while preserving the output command. Do not leave an unverified scale change in logic that drives the 4–20 mA module. Make the permanent repair in the display path, document the implied decimal convention, and test fractional values before restoring the meter.
Check: Monitor the value on both sides of each scale and conversion instruction. The BCD result must encode the intended scaled digits, not a value rounded or truncated by an earlier operation.
Configure the numeric display for one fractional digit
Set the numeric display to show one fractional digit when its input is an integer representing tenths. The fractional digit is a formatting convention; it does not convert an arbitrary binary or REAL value into BCD, and it does not correct the PLC's scaling.
Bind the object to the verified display value, not automatically to the output module's V-memory address. Confirm the object's data format and digit settings in the C-more Micro project. Exact menu names and supported formats vary by editor version, so use the installed project editor's object configuration rather than assuming a setting label.
- Open the numeric display object properties.
- Confirm the source address and the expected input format.
- Set one fractional digit for the tenths-scaled value.
- Download or apply the project using the normal controlled process.
Check: Compare a known PLC value with the displayed value. For an integer-tenths source of 123, the numeric object should present 12.3 under that convention.
Scale the analog meter to the same engineering value
An analog meter object needs a meaningful relationship between its input and its displayed range; showing a fractional digit on a numeric display does not automatically scale the meter. Feed it a verified value with a defined relationship to the quantity being indicated, and configure its range to match that value using the options in the project editor.
Do not assume the 4–20 mA output command equals an engineering measurement or that its raw counts map directly to the meter's scale. Read the module configuration and the PLC logic that generates the command to determine the actual range and units. If the meter reads BCD, provide a valid BCD value after scaling; if the editor offers a different supported representation, configure and test it explicitly.
Check: Test a low, middle, and high value across the actual configured span. Confirm the numeric display and meter move consistently and that changing display scaling does not alter the analog output command.
Verify the complete display and output path
Before returning the HMI to service, verify the chain with values whose expected display is known. Include at least one value with a nonzero tenths digit; whole-number-only tests will not expose an implied-decimal mismatch.
- Record the source value and its units.
- Check the scaled integer and BCD result in the PLC.
- Confirm the numeric display shows the intended tenths value.
- Confirm the meter indicates the same engineering quantity across its configured span.
- Confirm the 4–20 mA output command remains at its intended value while display logic runs.
Check: Accept the repair only when the PLC representation, numeric display, meter indication, and analog output command agree with their documented scales.
Frequently asked questions
What happens if I set one fractional digit but the value is not scaled?
The display places a decimal point according to its formatting; it does not create the missing tenths scale. Check the integer value and its implied units before relying on the displayed magnitude.
What happens if the PLC data view shows a real number?
That confirms the PLC can display or calculate that value in the data view, not that the C-more Micro object accepts REAL data. Verify the object's input format and provide a compatible scaled value.
What happens if the numeric display works but the meter is still wrong?
Check the meter's source address and configured range independently; numeric fractional formatting does not set the meter scale. Stop if the display value shares logic with the analog output and you cannot prove the output remains correct, then contact official C-more Micro or PLC support with the project, address mapping, and monitored values.