Single-Turn Precision Potentiometers

The following section will discuss the piece parts, assembly and features of multi-turn potentiometers. Highlights of each model family will also be reviewed. Am exploded view of a typical single-turn precision potentiometer is illustrated in Figure 11.9.

Figure 11.9

Housing

The housing for a single-turn precision potentiometer can be fabricated from machined metal or molded plastic. Plastic housings are lower in cost as compared to metal housings. Metal housings may give the product a more rugged package, however, either housing will give the end-user a highly reliable product.

Resistive Elements

Single-turn precision resistive elements are fabricated using thick-film silkscreen technology. The resistive ink may be conductive plastic or cermet (a combination of fine ceramic or glass particles with precious metals). Conductive plastic ink is used to achieve the long rotational life. The termination print is achieved with low resistance metallic inks. A typical resistive element is illustrated in Figure 11.10. joints.

Figure 11.10

The outer terminals are connected to the termination print pads by one of several methods. The most common methods are solder or swage type

In order to achieve the precision linearity performance, the elements go through a laser trimming operation.

Terminals

Turret style terminals are utilized in the single-turn precision models. Plastic molded housings typically have the terminals molded into the rear of the housing. Metal housings typically have the terminals mounted through the sidewall of the housing. Some models with metal housing will have a rear plastic cover which doubles as the element. In this case, the terminals will be molded into the cover.

Shaft Rotor Assembly

The shaft-rotor assembly for single-turn thick-film element models is much more simple as compared to the wirewound models. Models with a plastic shaft normally have a single piece molded shaft/rotor whereas models with a metal shaft will have the shaft swaged or molded to a plastic rotor. A contact spring is mounted to the rotor, which makes mechanical and electrical contact with the resistive element.

Mechanical/Electrical Function

A voltage is applied across the element (TR) terminals with the wiper terminal functioning as a variable voltage tap.

Turning the shaft rotates the rotor/contact spring assembly. The contact spring makes contact with the element and moves along the circular printed pattern producing a change in resistance. As the wiper contact moves along the resistive element, voltage is tapped off of the element and transmitted through the contact fingers to the collector ring and out through the wiper terminal.

Single-turn precision potentiometers are continuous-turn devices. There are options available in each of these models for a mechanical stop should it be required by your customer's application.

Mounting Methods

As with the multi-turn precision potentiometers, the single-turn versions offer the same mounting capabilities:

• Servo mount is used in applications where the potentiometer shaft is coupled to a motor or other mechanical driven applications
• Bushing mount is used in applications where the potentiometer shaft is mounted through a front panel and is to be adjusted manually