Connecting Arc Products to Programmable Logic Controllers (PLCs)
Wiring schematics and tips for connecting Arc sensors directly to programmable logic controllers.
Hamilton Arc intelligent sensors offer increased flexibility when connecting with process control systems (PCS). With this flexibility there can be some confusion about how to connect the sensors. This article explores the wiring connection options for Arc sensors and some practical considerations when connecting these products to programmable logic controllers (PLC).
PLC Considerations
Hamilton Arc and VisiFerm DO sensors generate the 4 - 20mA signal using pulse width modulation (PWM). In 3-wire configurations this form of analog output may generate signal noise on un-isolated PLC inputs. In these cases, Hamilton recommends a galvanic isolation amplifier between the sensor and the PLC input. A list of recommended isolation devices is provided below.
Additionally, Many PLCs are passive devices. 24VDC power required for the Arc sensor is supplied from a separate source. The wiring diagrams below account for installations such as this.
PLC Considerations
Hamilton Arc and VisiFerm DO sensors generate the 4 - 20mA signal using pulse width modulation (PWM). In 3-wire configurations this form of analog output may generate signal noise on un-isolated PLC inputs. In these cases, Hamilton recommends a galvanic isolation amplifier between the sensor and the PLC input. A list of recommended isolation devices is provided below.
Additionally, Many PLCs are passive devices. 24VDC power required for the Arc sensor is supplied from a separate source. The wiring diagrams below account for installations such as this.
Galvanic Isolation Amplifiers
Galvanic isolation amplifiers are recommended in 3 wire, 4-20mA installations where the PLC has no input isolation of its own. Hamilton recommends that the PLC sampling rate be set below 3.5 kHz with signal averaging > 1 second. Recommended suppliers are listed below.
- BasicLine BL 510 (Preferred)
- Knick B13000F1-S002 (Similar equivalent card is BL 510)
- Knick P15000 F1
- Knick P27000 H1
- Phoenix Contact MCR-SL-UI-UI active
- Phoenix Contact MCR-C-I//-00-DC active
Connection Options
4 - 20mA, 2-wire connection
This wiring scheme is suitable for polarographic DO, pH, ORP, and conductivity Arc sensors. It cannot be used with with the VisiFerm or with Wi Wireless Adapters due to the need for increased power consumption. No galvanic isolation is needed in this wiring scheme.
| VP Pin | Wiring (VP8) | Wiring (Data Cable) |
|---|---|---|
| Pin B | Coax shield, Black | Green |
| Pin D | Coax shield, Red | Blue |
4 - 20mA, 3-wire connection
A 3-wire connection with galvanic isolation between the sensor and PLC is shown above. This is the most frequent wiring scheme for direct connection to PLCs with no internal isolation of their input circuit.
| VP Pin | Wiring (VP8) | Wiring (Data Cable) |
|---|---|---|
| Pin B | Coax shield, black | Green |
| Pin C | Coax core, red clear | Red |
| Pin D | Coax shield, red | Blue |
4 - 20mA, 2-wire connection
This wiring scheme is suitable for polarographic DO, pH, ORP, and conductivity Arc sensors. It cannot be used with with the VisiFerm or with Wi Wireless Adapters due to the need for increased power consumption. No galvanic isolation is needed in this wiring scheme.
| VP Pin | Wiring (VP8) | Wiring (Data Cable) |
|---|---|---|
| Pin B | Coax shield, Black | Green |
| Pin D | Coax shield, Red | Blue |
Wiring for the Arc Wi 1G Wireless Adapter BT
Adding the Arc Wi 1G Wireless Adapter allows Modbus and 4 - 20mA signal as well as sensor specific outputs such as ECS. Galvanic isolation should be considered if the 4 to 20mA output is used.
| VP Pin | Wiring (VP8) | Wiring (Data Cable) |
|---|---|---|
| Pin B | Coax shield, black | Green |
| Pin C | Coax core, red clear | Red |
| Pin D | Coax shield, red | Blue |
| Pin G | Yellow | Grey |
| Pin H | Brown | Pink |
Wiring for the Arc Wi 2G Wireless Adapter BT
Arc Wi 2G Wireless Adapters include galvanic isolation of the 4 - 20mA outputs. No additional isolator is required. This design is the best choice for Arc sensor installations where wireless communication is desired.
| Pin | Wiring | Pin | Wiring |
|---|---|---|---|
| Pin 1 | White | Pin 6 | Pink |
| Pin 2 | Brown | Pin 7 | Blue |
| Pin 3 | Green | Pin 8 | Red |
| Pin 4 | Yellow | Ground | Green/Yellow |
| Pin 5 | Grey |
Related Content
- Hamilton has two Arc Wi Wireless Bluetooth Adapters. Learn the differences between the Arc Wi 1G and 2G Adapters.
- Local displays from other vendors can also be used with Arc sensors.