Download “Connecting Sensors to Interstacks” PDF
There are thousands of sensors for every possible application available from many sources. Please check with your support engineer for the sensors you want to connect to Interstacks. We resell some and can recommend many others. Your Interstacks support engineer can look at the data sheets and manuals to advise on compatibility. This document describes how to connect various types of sensors to Interstacks blocks.
Power for Sensors
The first thing you must do is determine how to power a sensor.
Some sensors, like the CT power sensors we resell, are self powered, meaning they do not require external power. Other sensors require 5V DC external power. A stack can supply 5v DC power out on pin 9 of the Analog In and I/O Expander blocks to power those 5V sensors.
The majority of standard industrial sensors often need to be powered externally with 10-30V DC, which cannot be supplied from the stack. There are often 24V DC supplies available in many factories for powering sensors. There are also many external small, inexpensive 12V wall power bricks that are available from many suppliers, including Interstacks, to power sensors externally. When powering sensors with an external supply, the Ground for that external supply must be connected to the sensor Ground and the stack ground (pin 10 on the Analog In, or I/O Expander block).
Dry Contact Switches
Dry contact switches (mechanical open/close switches or relay dry contact pins) connect to the Interstacks I/O Expander block. One wire goes to stack ground on pin 10, and one wire goes to one of the eight I/O Expander input channels. All switches must have one wire connected to the Ground pin.
Optical or other NPN output Switches
Some sensors that act as binary switches are not mechanical. Binary sensors that have a NPN output stage can be connected to the Interstacks I/O Expander block. (Sensors with PNP output stages cannot be connected). Optical proximity switches or optical “break beam” switches are often used to count machine cycles or parts. The NPN output stage versions can be used. Ground for the sensor connects to the stack Ground on pin 10 of the I/O Expander. The sensor output connects to any input channel on the I/O Expander. Ground from the external sensor power supply connects to the stack Ground on pin 10 and to the sensor Ground pin.
Digital Inputs – 24V
Binary signals that are 0V or 24V DC are often used in automation systems. The Interstacks Digital In block has four opto isolated input channels. Each input channel has its own Ground pin paired with it to avoid any Ground loop issues. Therefore each input channel signal must have its paired Ground pin connected to a Ground. The Grounds on the DIgital IN block are NOT connected to each other.
Analog 0-5V or 0-10V DC
Many sensors output an analog signal proportional to some physical characteristic like pressure or tank level. The analog voltage ranges are typically 0 to 5V DC or 0 to 10V DC. These sensors connect to the Interstacks Analog In block. Each pin of the Analog In block can be individually configured for many different analog interfaces. Ground for the sensor connects to the stack Ground on pin 10 of the Analog In block. The sensor output connects to one of the eight input channels on Pin 1-8. If the sensor is powered externally, the Ground for that power supply must be connected to the stack Ground pin 10 and the sensor Ground.
Analog 4-20 mA
Some analog sensors do not output a variable DC voltage but use a 4-20mA current loop interface. These sensors also connect to the Interstacks Analog In block. Each pin of the Analog In block can be individually configured for many different analog interfaces. Because 4-20mA sensors operate in an electrical loop, their wiring is different than variable DC voltage analog sensors. Ground for the external sensor power supply connects to the stack Ground pin 10. DC out from the external supply connects to the 4-20mA Sensor plus pin. The minus pin of the sensor goes to an input channel on the Analog In block. The wiring diagram below shows the electrical “loop”.
Note that pin 7 in this diagram is just an example of any of the 1-8 input channels.
Thermocouples
Thermocouples are special temperature sensors typically used for very high temperatures and cannot be directly connected to Interstacks blocks. You need to use a small interfacing device called a “transmitter”. Transmitters are widely available and inexpensive. They take the native thermocouple voltage and translate it to typically a 4-20mA analog signal. Make sure you order a transmitter that matches the type of thermocouple you want to use (J, K, N etc.).
Flow Meters – Rotary Encoders
Flow meters and rotary encoders output a digital pulse train proportional to liquid flow or rotation. They are often interfaced just like mechanical switches to the I/O Expander block. The variable digital pulses are accumulated in the stack software and then sent out as tag values.
Serial Data Interfaces – UART, RS232, RS485
Some devices, like scales, use serial data stream interfaces. If the device needs a 3.3v or 5v level serial digital interface, it connects to the Interstacks Serial block using the UART pins. If it uses a RS232 digital serial interface, it connects to the Interstacks RS232 block via its DB9 connector. If it uses a RS485 digital serial interface, it connects to the Interstacks RS485 block. RS485 is often used with a message protocol called Modbus RTU.
Serial
RS-485
RS-232
2 Receive 3 Transmit 5 Ground
GPS Receivers
GPS receivers connect to the Interstacks Serial block using its UART pins. We resell a GPS receiver on our web site and the message protocol is very standard.
Barcode Scanners
Barcode scanners (and some keyboards) connect to the Interstacks Barcode or Keyboard block using a USB-A connector.
Questions
To learn more about how Interstacks can help you harness your data and insights to drive better business outcomes, visit interstacks.com or contact our team directly to discuss your business operations and goals.