Electrolytic tilt sensors

The Fredericks Co., Huntingdon Valley, PA. 215-947-2500; www.frederickscom.com.

Figure 1

Suppose you need to measure an angle electronically. Your first attempt might involve attaching a weighted pendulum to a potentiometer so you could measure the varying resistance as the potentiometer moves. Or you could use the potentiometer in a bridge and measure the resulting voltage. The angle-measuring sensors built by Fredericks Co. use a similar principle, but instead of a fixed resistor and a wiper, they use a liquid in a sealed container (Figure 1).

The sensor's liquid includes an electrolyte that conducts electrons between a common connection and left and right electrodes. When the sensor undergoes a tilting motion, more electrolyte touches one electrode than the other, and the difference in current flow through each electrode represents the sensor's angle (Figure 2). The circuitry produces a nonlinear voltage difference you

Figure 2

The circuits that work with this type of electrochemical liquid sensor must use an AC current to prevent electrolysis at the electrodes. A DC current would degrade or destroy the sensor. If an application needs a DC output, though, you can place the sensor in a rectified bridge that produces a differential DC voltage. The sensors come in a variety of packages and offer various characteristics. Typical sensors operate over ranges from ±1° to 360°, and they have a time constant of under a second. You can get sensors that resolve minutes or seconds of angular displacement.

The manufacturer also supplies dual-axis sensors that use one common central electrode and four other electrodes equally spaced at 90°

Figure 3