fix Stanford Research SR830 output conversion (#1069)

* fix Stanford Research SR830 output conversion

* remove expand from output conversion

By testing with hardware I found that the expand value should not be included in the equation inside the output_conversion function. It seems the logic in the manual applies only to the analog output. The return value of the "OUTP?1" command is not effected by the expand factor!

* add protocol tests for selected getters and the output_conversion

* fix linter errors

pymeasure/instruments/srs/sr830.py

@@ -436,9 +436,9 @@ def output_conversion(self, channel):
         """ Returns a function that can be used to determine
         the signal from the channel output (X, Y, or R)
         """
-        offset, expand = self.get_scaling(channel)
+        offset, _ = self.get_scaling(channel)
         sensitivity = self.sensitivity
-        return lambda x: (x / (10. * expand) + offset) * sensitivity
+        return lambda x: x + offset / 100 * sensitivity
 
     @property
     def sample_frequency(self):

tests/instruments/srs/test_sr830.py

@@ -0,0 +1,95 @@
+#
+# This file is part of the PyMeasure package.
+#
+# Copyright (c) 2013-2024 PyMeasure Developers
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+#
+import pytest
+
+from pymeasure.test import expected_protocol
+from pymeasure.instruments.srs.sr830 import SR830
+
+
+def test_id():
+    """Verify the communication of the device type."""
+    with expected_protocol(
+        SR830,
+        [("*IDN?", "Stanford_Research_Systems,SR830,s/n12345,ver1.07"),],
+    ) as inst:
+        assert inst.id == "Stanford_Research_Systems,SR830,s/n12345,ver1.07"
+
+
+@pytest.mark.parametrize("number, value", (
+        ("0", 2e-9),
+        ("14", 100e-6),
+        ("25", 0.5),
+))
+def test_sensitivity(number, value):
+    """Verify the communication of the sensitivity getter."""
+    with expected_protocol(
+        SR830,
+        [("SENS?", number),],
+    ) as inst:
+        assert inst.sensitivity == pytest.approx(value)
+
+
+def test_frequency():
+    """Verify the communication of the frequency getter."""
+    with expected_protocol(
+        SR830,
+        [("FREQ?", "121.98"),],
+    ) as inst:
+        assert inst.frequency == pytest.approx(121.98)
+
+
+def test_snap():
+    """Verify the communication of the measurement values."""
+    with expected_protocol(
+        SR830,
+        [("SNAP? 1,2", "-4.17234e-007,-5.9605e-007"),],
+    ) as inst:
+        xy = inst.xy
+        assert len(xy) == 2
+        assert xy[0] == pytest.approx(-4.17234e-007)
+        assert xy[1] == pytest.approx(-5.9605e-007)
+
+
+def test_get_scaling():
+    """Verify the communication of the X channel scaling settings."""
+    with expected_protocol(
+        SR830,
+        [("OEXP? 1", "9.7,1"),],
+    ) as inst:
+        offset, expand = inst.get_scaling("X")
+        assert offset == pytest.approx(9.7)
+        assert expand == pytest.approx(10)
+
+
+def test_output_conversion():
+    """Verify the communication of the X channel value with conversion."""
+    with expected_protocol(
+        SR830,
+        [("OEXP? 1", "10,1"),
+         ("SENS?", "19"),
+         ("OUTP?1", "-0.000500266"),
+         ],
+    ) as inst:
+        conv = inst.output_conversion("X")
+        assert conv(inst.x) == pytest.approx(-2.66e-7)