StallGuard+ is an advanced sensorless load detection technology that measures mechanical load directly from the motor’s electrical behavior without external force sensors, encoders, or switches. The StallGuard+ algorithm monitors the motor’s real-time electrical operating point and calculates SGP_RESULT, a dimensionless load indicator.
In infusion pumps, occlusion detection is traditionally based on pressure sensing load cells or strain gauges pressed against compliant tubing.
When flow is obstructed, pressure inside the tubing gradually builds, causing the tubing to expand and apply force to the sensor. The pump monitors this pressure increase over time and triggers an alarm once a threshold or rate of rise condition is met. While effective, this approach can be very slow at low-flow rates, where pressure accumulates gradually.
When an occlusion such as a kinked line, clamped tube, or downstream blockage occurs, the resistance to fluid flow increases immediately. This increased resistance manifests as higher mechanical load on the motor, which, in turn, alters the motor’s current draw and electrical operating point. StallGuard+ detects this change directly, enabling the system to recognize abnormal load conditions.
Figure 4 shows that creating an occlusion by clamping the tubing caused the pressure to increase gradually while the StallGuard+ value decreased, showing a clear inverse correlation.
As the blockage worsened, StallGuard+ eventually reached zero, at this point software used the stall indication to stop the motor and trigger an alarm.
The strong inverse relationship between pressure and StallGuard+ values confirms that StallGuard+ is an effective sensor-free method for detecting occlusions, especially at low flow rates where conventional pressure-based alarms may respond more slowly. While it is not intended to completely replace pressure sensors, StallGuard+ serves as a valuable complementary diagnostic tool. It can help provide faster initial detection, redundancy for safety monitoring, or diagnostic insight in designs where pressure sensors are constrained by size, cost, or mechanical placement.
Applicable Part Numbers
| Digikey Part Number | Manufacturer Part Number |
|---|---|
| 175-TMC5262AFV±ND | TMC5262AFV+ |
| 175-TMC5262AFV+TTR-ND,175-TMC5262AFV+TCT-ND,175-TMC5262AFV+TDKR-ND | TMC5262AFV+T |
| 175-TMC5262-EVKIT-ND | TMC5262-EVKIT |