Action Instruments - Adjustable Clamp Application Note

Adjustable Clamp
By: Brad Cone, Applications Engineer

An engineer called with an interesting problem. He has an application that requires an offset of a 4-20 mA process signal. The problem he has is that his offset changes from time to time and he needs the ability to adjust the offset quickly and easily. He wants a device that provides an adjustable clamp to provide the offset.

This can be accomplished using two ActionPaks. An AP4003 and an AP4502. TheAP4502 is a high select module. It transmits the higher of two input signals. The AP4003 is a potentiometer to analog signal conditioner. A potentiometer is used to set the output to a desired level. The existing signal is connected to one channel of the AP4520, the AP4003 to the other. The AP4003 sets the offset clamp. For instance, if the AP4003 is set for a 10 mA output, the output of the AP4502 will stay at 10 mA when the process signal is below 10 mA and follow the process signal above 10 mA.

An AP4380 may be required on the output of the AP4502 if isolation is required in the system.

Last updated January 6, 2004