How do you use setpoints and relays?

When developing systems for automation or maintenance monitoring, acquiring highly accurate force data with a load cell is only the first step. To be able to react to this data, the sensor must be equipped with a Instrumentation They are combined with components that are capable of processing the signal and triggering mechanical reactions.

Interface Tech Talk explains the fundamentals of using setpoints and relays in force measurement programs and general testing applications. Understanding the specific functions of setpoints and relays, as well as their interaction with sensor hardware, is crucial for maintaining system safety and preventing [unclear]. overloads and the achievement of automation and test objectives.

The sensor base: From force to signal

Before an instrument can evaluate a setpoint, a strain gauge must be applied.load cell converting the physical force into an electrical process quantity. When a load acts on the sensor, the internal components deform. Strain gauges minimal, which changes its electrical resistance. This change is measured as an analog millivolt-per-volt (mV/V) signal.

Since this raw sensor signal is very small, it is processed via shielded cables. Cables  or  Wireless technologies The signal is transmitted to a coupled instrument. The instrument provides a clean excitation voltage to power the sensor, amplifies the incoming mV/V analog signal, and converts it into units of measurement such as pounds, kilograms, or newtons. Once the data is digitized, the instrument can execute logic based on programmed parameters.

TIPP: Read our article Raw Signals to Intelligent Force Sensing.

How setpoints work

A setpoint is a digital or software-based threshold value programmed into the instrumentation that corresponds to a specific measurement point. The instrument continuously compares the current, processed force measurements with this threshold value to determine, based on predefined criteria, whether an action is required.

Configuration options

• High target value It is activated when the force exceeds the threshold. This is standard practice for protecting structures from overload, setting safety limits on cranes, or stopping an assembly press before it damages a component.
• Low setpoint It is activated when the force falls below the threshold. It is frequently used for slack rope detection in cable tension monitoring or for identifying an empty material container.
• Band or window setpoint It defines a permissible operating range, limited by an upper and a lower limit. The system monitors whether the current force is within or outside this predefined window.

Hysteresis limits

To prevent rapid, damaging switching of external hardware when a load fluctuates minimally around the threshold, instruments use a mathematical buffer called the HysteresisThe hysteresis sets a secondary reset threshold. For example, if a high setpoint of 5.000 pounds is configured with a hysteresis of 50 pounds, the trigger will activate precisely at 5.000 pounds but will not deactivate until the force drops below 4.950 pounds. This protects downstream electronics and mechanical switches from chatter caused by signal noise or physical vibrations.

How relays work

While the setpoint represents the logical condition evaluated by the instrument, the relay is the physical or electronic switch that performs the mechanical work. When a setpoint condition is met, the instrumentation sends a signal to change the operating state of the relay, thereby opening or closing an external circuit. There are two basic relay technologies:

• Electromechanical relays (EMR): These devices use an internal electromagnetic coil to physically actuate mechanical contacts. EMRs offer excellent electrical isolation and can switch high currents, making them ideal for switching heavy motors or large pneumatic valves. They have a limited physical lifespan and switch in milliseconds.
• Solid-state relays (SSRs): These devices use semiconductor components to switch electrical circuits electronically without moving parts. SSRs offer high-speed operation, long lifespan, and are ideally suited for rapid material testing or high-frequency dispensing applications.

Relays have two basic states when de-energized:

• Normally Open (NO) – Normally open: The circuit remains open until a setpoint condition forces the relay to close, thus completing the path to supplying an external device.
• Normally Closed (NC) – Normally closed: The circuit carries current continuously until a setpoint condition forces the relay to open, thus interrupting the path to switch off active machines.

Instrumentation integration and selection

Selecting the right instrumentation for your load cell ensures that setpoints are evaluated at the required speed and relays switch reliably under application load. Interface offers a wide range of instrumentation options to manage these requirements and control loops.

Interface 920i Programmable Weight Indicator and Controller

The interface 920i Programmable Weight Indicator and Controller It is designed for complex industrial automation and dosing with multiple sensors. It supports multiple independent setpoints, allowing operators to program sequential ingredient dispensing, monitor weight change rates, and connect physical relay outputs directly to industrial actuators. For a complete system, we recommend our ILMP 920i System.

Interface 480 Weight Indicator

For simple security monitoring and threshold tracking, the interface offers 480 Bidirectional Weight Indicator Robust setpoint configurations with standard digital outputs. Combined with a low-profile strain gauge load cell, the 480 monitors forces in real time and triggers its internal relays to immediately stop hydraulic or mechanical systems as soon as an overload threshold is exceeded.

Interface BSC4A Multi-channel signal conditioner

In applications with multi-axis load cells or several separate sensors condition the BSC4A Multi-channel analog output bridge amplifier Up to four channels simultaneously. It allows engineers to define individual setpoint logic across different axes and to ensure that a force anomaly on a secondary axis immediately triggers a system-wide shutdown via its integrated digital outputs.

TIPP: For further information, we recommend our Instrumentation Webinar, which presents products and ideal combinations based on system requirements.