OpenModelica
Unit mismatch error although units are the same
I have an .ssp with a SystemStructure.ssd file that has an .fmu with unit = "" on all outputs in its ModelDescription file. When I add unit to one of these connectors in SystemStructure.ssd: <ssd:Connector name="pLin.in.y" kind="output" description=""> <ssc:Real unit="bar"/> </ssd:Connector>
and connect this connector to another connector in the .ssd with the same unit:
<ssd:Connector name="pLin" kind="input" description="Input load pressure"> <ssc:Real unit="bar"/> </ssd:Connector>
<ssd:Connection endConnector="pLin" endElement="valve_model" startConnector="pLin.in.y" startElement="interface_model"/>
I get error:
error: [addConnection] Unit mismatch in connection: interface_model.pLin.in.y -> valve_model.pLin error: [importFromSnapshot] Failed to import ssd:Connection
If I instead have
<ssd:Connector name="pLin.in.y" kind="output" description=""> <ssc:Real unit=""/> </ssd:Connector>
I get no error.
Should not the units in the ssd override the units in the FMU?
Also, the fmu for valve_model has units on all connectors.
My ssp as zip: ParkerSimPack.zip
Running OMiImulator python api, version 'OMSimulator v2.1.3-win-notlm'
an empty unit in Modelica is not treated the same as unit 1, need to check the specification to know how this is supposed to be handled
@lochel @arun3688 @lenaRB I tried now with latest version of OMSimulator ('OMSimulator v3.0.0.post103-g53bba5e-win') and it seems to work. Can you confirm that this is fixed, and if so how is it now handled?
@larsviktorlarsson How should I test this?
When I run the attached SSP file with the latest OMSimulator [1], I get the following errors:
error: [addConnection] Unit mismatch in connection: interface_model.pLin.in.y -> valve_model.pLin
error: [importFromSnapshot] Failed to import ssd:Connection
I’m not sure whether this behavior is intended. I need to take a closer look at the SSP package and the FMUs to understand how the units are defined.
Do you have a Python or Lua script that can be used to test the different cases?
[1] OMSimulator v3.0.0.post120-g9acb585-linux-debug
@lochel When I created the issue I ran an older version (<3.0) where the syntax was different from now. If I use a newer version [1] with the following (first change the file ending from .zip to .ssp on ParkerSimPack) python script:
from OMSimulator import SSP
model = SSP('ParkerSimPack.ssp')
I get the following error:
AttributeError Traceback (most recent call last) File c:\parker\python\omstroubleshoot\oms_error.py:10 2 """ 3 Created on Mon Jan 12 16:42:34 2026 4 5 @author: vicla25 6 """ 8 from OMSimulator import SSP ---> 10 model = SSP('ParkerSimPack.ssp')
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\ssp.py:33, in SSP.init(self, path, temp_dir) 30 logger.info(f"Temporary directory created: {suppress_path_to_str(self.temp_dir)}") 32 if path: ---> 33 self._extract_ssp(path) 35 # Ensure at least one variant exists 36 if self.activeVariantName is None:
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\ssp.py:70, in SSP._extract_ssp(self, path) 68 for ssd_file in ssd_files: 69 ssd_path = self.temp_dir / ssd_file ---> 70 ssd = SSD.importFromFile(ssd_path, self.resources) 71 self.add(ssd)
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\ssd.py:42, in SSD.importFromFile(filename, resources) 40 root = tree.getroot() 41 filename = Path(filename).resolve() ---> 42 return SSD.importFromNode(root, filename, resources) 43 except ET.ParseError as e: 44 logger.error(f"Error parsing SSD file '{filename}': {e}")
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\ssd.py:67, in SSD.importFromNode(root, filename, resources) 65 if system is None: 66 raise ValueError(f"Invalid SSD file: Missing ssd:System in {filename}") ---> 67 ssd.system = System.importFromNode(system, ssd, resources) 68 utils.parseDefaultExperiment(root, ssd) 69 Unit.importFromNode(root, ssd)
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\system.py:117, in System.importFromNode(node, ssd, resources) 115 system.systemgeometry = SystemGeometry.importFromNode(node) 116 utils.parseParameterBindings(node, system, resources) --> 117 system.elements = utils.parseElements(node, resources) 118 system.solvers = utils.parseAnnotations(node) 119 Connection.importFromNode(node, system)
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\utils.py:85, in parseElements(node, resources) 83 elements[name].connectors = Connector.importFromNode(component) 84 elements[name].elementgeometry = ElementGeometry.importFromNode(component) ---> 85 parseParameterBindings(component, elements[name], resources) 86 solvers = parseAnnotations(component) 87 if solvers:
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\utils.py:127, in parseParameterBindings(node, obj, resources) 124 for mapping in parameter_mapping_ssm.findall("ssm:MappingEntry", namespaces=namespace.ns): 125 obj.parameterMapping.mapParameter(mapping.get("source"), mapping.get("target")) --> 127 Unit.importFromNode(param_set, obj, tagname="ssv:Units")
File C:\ProgramData\anaconda3\Lib\site-packages\OMSimulator\unit.py:29, in Unit.importFromNode(node, root, tagname) 27 @staticmethod 28 def importFromNode(node, root, tagname = "ssd:Units"): ---> 29 units_element = node.find(tagname, namespaces=namespace.ns) 30 if units_element is None: 31 return
[1] 'OMSimulator v3.0.0.post116-g5158e1a-win'
So the error is not exactly the same, but still something is off with the units.