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AsCressbessman
AsCress
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bessman
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feat: Improved algorithm for measuring capacitance
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4 files changed

+16
-42
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4 files changed

+16
-42
lines changed

‎pslab/instrument/multimeter.py

Lines changed: 13 additions & 39 deletions
Original file line numberDiff line numberDiff line change
@@ -31,7 +31,7 @@ class Multimeter(Oscilloscope):
3131
_CAPACITOR_DISCHARGED_VOLTAGE = 0.01 * max(INPUT_RANGES["CAP"])
3232

3333
def __init__(self, device: SerialHandler = None):
34-
self._stray_capacitance = 5e-11
34+
self._stray_capacitance = 46e-12
3535
super().__init__(device)
3636

3737
def measure_resistance(self) -> float:
@@ -125,48 +125,22 @@ def measure_capacitance(self) -> float:
125125
Capacitance in Farad.
126126
"""
127127
for current_range in self._CURRENTS_RANGES:
128-
for i, charge_time in enumerate([50000, 5000, 500, 50, 5]):
129-
voltage, _ = self._measure_capacitance(current_range, 0, charge_time)
130-
131-
if voltage < self._CAPACITOR_CHARGED_VOLTAGE:
132-
if i:
133-
return self._binary_search_capacitance(
134-
current_range, charge_time, charge_time * 10
135-
)
136-
else:
137-
break # Increase current.
128+
charge_time = 10
129+
for _ in range(10):
130+
if charge_time > 50000:
131+
break # Increase current.
132+
voltage, capacitance = self._measure_capacitance(
133+
current_range, 0, charge_time
134+
)
135+
if 0.98 < voltage / self._CAPACITOR_CHARGED_VOLTAGE < 1.02:
136+
return capacitance
137+
charge_time = int(
138+
charge_time * self._CAPACITOR_CHARGED_VOLTAGE / voltage
139+
)
138140

139141
# Capacitor too big, use alternative method.
140142
return self._measure_rc_capacitance()
141143

142-
def _binary_search_capacitance(
143-
self,
144-
current_range: int,
145-
low_charge_time: int,
146-
high_charge_time: int,
147-
) -> float:
148-
charge_time = (high_charge_time + low_charge_time) // 2
149-
voltage, capacitance = self._measure_capacitance(
150-
current_range,
151-
0,
152-
charge_time,
153-
)
154-
155-
if voltage / self._CAPACITOR_CHARGED_VOLTAGE < 0.98:
156-
return self._binary_search_capacitance(
157-
current_range,
158-
charge_time,
159-
high_charge_time,
160-
)
161-
elif voltage / self._CAPACITOR_CHARGED_VOLTAGE > 1.02:
162-
return self._binary_search_capacitance(
163-
current_range,
164-
low_charge_time,
165-
charge_time,
166-
)
167-
else:
168-
return capacitance
169-
170144
def _set_cap(self, state, charge_time):
171145
"""Set CAP HIGH or LOW."""
172146
self._device.send_byte(CP.ADC)

‎tests/recordings/multimeter/test_measure_capacitance.json

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1 +1 @@
1-
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1+
[[[2], [8], [1], [0], [2], [8], [2], [0], [2], [10], [5], [2], [21], [0], [80, 195], [2], [10], [5], [2], [21], [0], [80, 195], [2], [10], [5], [11], [2], [1], [0], [10, 0], [2], [10], [5], [11], [2], [1], [0], [139, 6], [2], [10], [5], [2], [21], [0], [80, 195], [2], [10], [5], [11], [2], [1], [0], [236, 21]], [[], [], [], [1], [], [], [], [1], [], [], [193, 225, 1], [], [], [], [1], [], [], [169, 2, 1], [], [], [], [1], [], [], [116, 0, 1], [], [], [], [], [22, 0, 1], [], [], [196, 0, 1], [], [], [], [], [76, 4, 1], [], [], [227, 61, 1], [], [], [], [1], [], [], [31, 1, 1], [], [], [], [], [31, 14, 1]]]

‎tests/recordings/multimeter/test_measure_resistance.json

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1 +1 @@
1-
[[[2], [8], [1], [0], [2], [8], [2], [0], [2], [10], [7]], [[], [], [], [1], [], [], [], [1], [], [], [157, 170, 1]]]
1+
[[[2], [8], [1], [0], [2], [8], [2], [0], [2], [10], [7]], [[], [], [], [1], [], [], [], [1], [], [], [118, 169, 1]]]

‎tests/recordings/multimeter/test_voltmeter_autorange.json

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1 +1 @@
1-
[[[2], [8], [1], [0], [2], [8], [2], [0], [2], [8], [1], [0], [2], [10], [3], [2], [8], [1], [7]], [[], [], [], [1], [], [], [], [1], [], [], [], [1], [], [], [71, 128, 1], [], [], [], [1]]]
1+
[[[2], [8], [1], [0], [2], [8], [2], [0], [2], [8], [1], [0], [2], [10], [3], [2], [8], [1], [7]], [[], [], [], [1], [], [], [], [1], [], [], [], [1], [], [], [255, 127, 1], [], [], [], [1]]]

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