Increased 'noise' immunity on injection machine control.

Increased |Noise' Immunity On Injection Machine Control

Modifications to increase immunity against in-plant electromagnetic "noise" reportedly have been completed on the Siemens Pathfinder EL control, which is offered by Van Dorn Plastics Machinery Co., Strongsville, Ohio, on its injection molding machines. These fixes were made specifically to address problems of control "lock-up" during the molding cycle, which were experienced by molders after the control's introduction to the marketplace in 1988 (see PT, May '88, p. 37).

Soon after becoming aware of the problem with the control, Siemens and Van Dorn jointly formed a team of engineers to identify the problems that the controls were experiencing in the field. The team identified the major source of the control's problem as electrical noise and voltage spikes in the operating environments, says Al Tolliver, Van Dorn's manager of customer service.

The next step, says Tolliver, was to identify the level of immunity needed by the control to protect it against electrical interference. To achieve that immunity level, Van Dorn says it has addressed both noise protection in the "firmware" - i.e., software that is specific to microprocessor modules within the control - and grounding and shielding of the communication lines.

First, Siemens upgraded the firmware by rewriting the microprocessor programs to increase the level of immunity of the microprocessor modules to noise. Also, Van Dorn determined that much of the noise was infiltrating the system between the operator panel and the central processing unit of the microprocessor. It then designed EMI shielding for the communications lines between those two points, as well as other connections in the control. It also improved the grounding for each machine, and recommends that an earth ground be in place for each machine in a plant.

BASIC ARCHITECTURE SOUND

Tolliver says that the remedies - through shielding, grounding, noise filtration, and firmware changes - have successfully addressed the problem of transient plant noise. He maintains that the Pathfinder EL control's basic architecture was sound at the time of introduction and required no modifications. Since identifying the problem, Van Dorn says that all of its machines shipped with the Pathfinder EL control have been equipped with the upgraded protection and all of the original firmware (Version 3.0) has been replaced through a field modification program.

Van Dorn says that lab testing of the control gave no hint of the noise sensitivity problem when the control was introduced. Because the noise problem of the EL control first became evident in customer plant environments after delivery, Van Dorn now requires "beta-site" (i.e., user-site) testing for all its newly developed products.

Van Dorn, which now has over 1000 EL controls in the field, declined to say how many failures occurred due to noise sensitivity. However, according to marketing manager Kenneth Vaughan, reliability studies have demonstrated a 40% improvement in mean time between failures from 1990 to 1991. The company set a goal of 1% or lower failure rate for the Pathfinder EL control, and says the Siemens control reached that goal this year.