| 摘要 |
<p>An electrical balance has a load receiving load pan, a circuit for supplying current pulses in dependence on the load being weighed, a summing means for counting the current pulses over respective predetermined time intervals to derive a quantity representing the weighing result, display means providing a digital indication thereof, and a control circuit for automatically predetermining the length of each time interval and for adapting the number of places of the indication at the display for either rapid rough weighing or at a higher sensitivity up to the maximum as the target weight is reached. The balance has a weighing chamber having a door, the opening and closing of which is arranged to effect switching of a control circuit so that when substance is being placed on the pan, and a switch is actuated by the open door to a de-sensitizing position, the large variations in the sensor circuit exceed thresholds of a pair of comparator circuits, causing shortening of integration time to for example, 0.02 seconds, instead of 2 seconds. The count of pulses is indicated lacking the last two digital positions, as a rough weighing. As the target weight is approached and minimal substance is added, the lesser deflection of the balance is sensed by the comparator circuits, causing a switch to be actuated to omit the last place only of the indication; finally when the door is closed a switching action restores the full resolution time and maximum sensitivity, i.e. slowest weighing.</p> |
