Providing analog capabilities for micro-PLCs
Paul Goodale, Design Engineer,
CALEX Mfg. Co. Inc., Concord, CA
Micro-PLCs are replacing electromechanical relays, timers, cam switches, and counters, and gaining analog capabilities. For micro-PLCs to continue to find OEM applications and add analog capabilities, engineers must find low-cost methods of converting analog variables into digital form.
All analog-to-frequency converters change the analog value into a pulse train that corresponds to a proportion of a sensor's range. Input modules include 0 to 10V, 4 to 20 mA, RTD, TC, and strain gauge. Output modules convert the PLC pulse output to 0 to 10V or 4 to 20 mA. Each module is a single-channel unit.
To measure temperatures by using thermocouples, users must employ special techniques, which can become expensive. CALEX's 8511 converter modules employ a nonlinear amplifier to compensate for nonlinearity in thermocouple outputs.
To contact a Calex Mfg. Co. Inc. applications engineer, call 800-542-3355 or fax 510-687-3333.
Polyketone: unique material for plastic gearing
John Kelley, Staff Research Engineer, Shell Chemical Company, Houston, TX
Made by Shell Chemical, CARILONģ Thermoplastic Polymers, a new family of engineering thermoplastics known as aliphatic polyketones (PKs), offer a unique balance of mechanical, tribological (friction and wear), chemical resistance, and injection-molding properties. This balance of properties uniquely positions PKs for plastic gearing when compared to polyamide (PA) and acetal (POM), the two engineering thermoplastic polymers (ETPs) most widely used for this application.
Polyketones have a broad range of chemical resistance, and absorb significantly less moisture than PAs, with negligible effect on gear performance properties and gear dimensions. In addition, PKs possess impact resistance superior to that of POMs, better creep resistance than PAs, and creep-rupture resistance superior to that of POMs. The creep and impact performance of PKs might offer some performance advantages for plastic gearing that abruptly runs into stalled conditions--for example, in some actuator applications.
The lubricity of PKs against themselves or steel appears higher than PAs and equivalent to or higher than POMs against themselves or steel. The wear resistance of PKs when run on steel in pure sliding also appears to exceed that of PAs and is equivalent to or better than POMs. Most importantly, the wear resistance of PKs, when run on themselves in pure sliding or rolling contact, is significantly better than PAs or POMs against themselves.
To speak with an applications engineer from Shell Chemical Co., call 800-CARILON.