Medical device with battery testing
A method and device for testing a battery that powers a body-wearable medical device. The battery is contacted via battery contacts and a capacitor is arranged in parallel with the battery contacts. During the battery test, a first capacitor voltage U 1 is determined at a first time t 1 and a second capacitor voltage U 2 is determined at a second time t 2 subsequent to time t 1 . A test current is drawn between time t 1 and time t 2 . t 1 is determined by the beginning of drawing the test current and time t 2 is determined such that the capacitor voltage at time t 2 is in a steady state and is substantially constant while the test current is being drawn. A charging state of the battery is determined from the difference in voltage between U 1 and U 2 and/or from a time difference between the time t 1 and time t 2.
1. A battery powered extracorporeal medical device configured to be attached to the body or carried close to the body of a user, the medical device comprising:
battery contacts configured to contact the battery;
a capacitor in parallel electrical arrangement with the battery contacts; and
a controller configured to control operation of the medical device, the controller including a battery tester configured to:
determine a first capacitor voltage U 1 at a first point in time t 1 ;
determine a second capacitor voltage U 2 at a second point in time t 2 subsequent to time t 1 ;
draw between time t 1 and time t 2 a test current, wherein time t 1 is determined by the beginning of drawing the test current and time t 2 is determined such that the capacitor voltage at time t 2 is in a steady state and substantially constant while the test current is being drawn; and
determine a charging state of the battery from the difference between the voltage U 1 and the voltage U 2 and/or from a time difference between time t 1 and time t 2 .
2. The medical device according to claim 1 , wherein the test current is drawn over a time period selected from the group consisting of over 15 sec., over 30 sec. and over 120 sec.
3. The medical device according to claim 1 , wherein the controller includes a computing circuit configured to execute a reference routine, wherein the test current is drawn by the computing circuit in response to the execution of the reference routine.
4. The medical device according to claim 1 , wherein the battery tester includes a low-pass filter and is further configured to determine the capacitor voltage by low-pass filtering a voltage drop over the capacitor.
5. The medical device according to claim 4 , wherein the low-pass filter is a Finite Input Response (FIR) filter.
6. The medical device according to claim 5 , wherein the low-pass filter is a moving average filter.
7. The medical device according to claim 1 , wherein the battery tester is configured, while the test current is drawn, to continuously monitor the capacitor voltage and to determine time t 2 from the monitored capacitor voltage.
8. The medical device according to claim 7 , wherein the battery tester is configured to determine time t 2 by determining that a variation of the capacitor voltage does not exceed a predetermined voltage variation threshold for a predetermined time period.
9. The medical device according to claim 7 , wherein the battery tester is configured to cancel the ongoing battery test and stop drawing the test current if a steady state of the capacitor voltage is not reached within a timeout interval after time t 1 .
10. The medical device according to claim 1 , wherein the battery tester is configured to determine, prior to executing a battery test, whether the capacitor voltage is steady and is further configured to not execute the battery test if the battery voltage is unsteady.
11. The medical device according to claim 1 , further comprising a step-up voltage converter, wherein the test current is drawn at the high-voltage side of the step-up voltage converter.
12. The medical device according to claim 1 , wherein at least one of the battery contacts is a contact spring that holds the battery in a floating manner.
13. The medical device according to claim 1 , further comprising at least one of an insulin pump and a continuous glucose measurement device.
14. The medical device according to claim 1 , wherein, at time t 1 , the first capacitor voltage U 1 corresponds to the voltage of the capacitor when initially connecting a test load to the battery and the capacitor to draw the test current and before the voltage of the capacitor has significantly changed due to drawing the test current; and, at time t 2 , the voltage of the capacitor has stabilized within tolerance limits while still drawing the test current.
15. A method for testing a battery that powers a body-wearable medical device, the battery being contacted via battery contacts and a capacitor arranged in parallel electrical arrangement with the battery contacts, the method comprising:
determining a first capacitor voltage U 1 at a first point in time t 1 ;
determining a second capacitor voltage U 2 at a second point in time t 2 subsequent to the first point in time t 1 ;
drawing, between time t 1 and time t 2 , a test current, wherein time t 1 is determined by the beginning of drawing the test current and wherein time t 2 is determined such that the capacitor voltage at time t 2 is in a steady state and substantially constant while the test current is being drawn;
determining a charging state of the battery from the difference in voltage between U 1 and U 2 and/or from a time difference between the time t 1 and time t 2 .
16. The method according to claim 15 , wherein the test current is drawn over a time period selected from the group consisting of greater than 15 sec., greater than 30 sec. and greater than 120 sec.
17. The method according to claim 15 , further comprising executing a reference routine by a computing circuit, wherein the test current is drawn by the computing circuit in response to the execution of the reference routine.
18. The method according to claim 15 , wherein the method includes determining the capacitor voltage by low-pass filtering a voltage drop over the capacitor.
19. The method according to claim 18 , wherein the low-pass filtering is carried out with a Finite Input Response (FIR) filter.
20. The method according to claim 19 , wherein the low-pass filtering is carried out with a moving average filter.
21. The method according to claim 15 , further comprising, while the test current is drawn, continuously monitoring the capacitor voltage and determining time t 2 from the monitored capacitor voltage.
22. The method according to claim 21 , further comprising determining time t 2 by determining that a variation of the capacitor voltage does not exceed a predetermined voltage variation threshold for a predetermined time period.
23. The method according to claim 21 , further comprising cancelling the ongoing battery test and stopping the drawing of the test current when a steady state of the capacitor voltage is not reached within a timeout interval after time t 1 .
24. The method according to claim 15 , further comprising:
determining, prior to executing the battery test, whether the capacitor voltage is steady; and
not executing the battery test when the battery voltage is unsteady.
25. The method according to claim 15 , further comprising drawing the test current at the high-voltage side of a step-up voltage converter.
26. The method according to claim 15 , wherein the body-wearable medical device includes at least one of an insulin pump and a continuous glucose measurement device.
27. The method according to claim 15 , wherein, at time t 1 , the first capacitor voltage U 1 corresponds to the voltage of the capacitor when initially connecting a test load to the battery and the capacitor to draw the test current and before the voltage of the capacitor has significantly changed due to drawing the test current; and, at time t 2 , the voltage of the capacitor has stabilized within tolerance limits while still drawing the test current.