Bubble Sensors – Test Pin

AX1X Sensors

The test pin is enabled on all SMD AX1X bubble sensors (e.g. A210, A215, A310, etc.). The sensor has an internal 10kOhm pull-up resistor on the Test pin, to prevent a “Floating” condition on the line.

Pulling the test pin to 3.3-5VDC internally disables the transmitter portion of the circuit while the test pin is high.

If the transmitter is disabled, you should expect to see an “air” output under all circumstances – if you see a 5V output while the test pin is pulled high then there is something wrong with the circuit. The sensor is not detecting bubbles while the test pin is high so if you’re checking the test pin during device operation, ideally you should only pull the test pin high for a short amount of time (for example 1 to 2 100 microsecond cycles). The Test input may be used to force an Air-in-line condition while liquid is present.

The table below summarizes the output logic of AX1X bubble sensors

AX1X Bubble Sensor Logic

AX3X and AX4X Bubble Sensors

SMD Bubble Sensors have an optional test pin that is often required for medical device applications. On our standard sensors, the last digit of the part number denotes whether the test pin is enabled or disabled:

• “E-Type” sensors (e.g. A430-SLTE) have the test function enabled.
• “D-Type” sensors (e.g. A430-SLTD) have the test function disabled.

If the test function is enabled, the test pin (typically white wire) must be grounded for normal operation. Pulling the test pin to 5VDC internally disables the transmitter portion of the circuit while the test pin is high.

If the transmitter is disabled, you should expect to see an “air” output under all circumstances – if you see a 5V output while the test pin is pulled high then there is something wrong with the circuit. The sensor is not detecting bubbles while the test pin is high so if you’re checking the test pin during device operation, ideally you should only pull the test pin high for a short amount of time (for example 1 to 2 50 microsecond cycles). The Test input may be used to force an Air-in-line condition while liquid is present. This may help simplify the setups for EMI/EMC testing as both Air-in-line, and Liquid-in-line states may be tested with a single tubing configuration.

Do not apply more than 5VDC to the test pin of any bubble sensor, regardless of the input voltage of the sensor.

The tables below summarize the output logic of bubble sensors with test pin disabled and test pin enabled.

Bubble Sensor Logic – Test Function Disabled

Bubble Sensor Logic – Test Function Enabled