pH sensors

How do I connect an intelligent pH or ORP sensor to a traditional bioreactor?

Most bioreactors are developed around traditional pH / ORP sensors. Because of this, users may not consider Arc intelligent pH sensor technology due concerns about connectivity with the bioreactor. This article explores ways to make this connection so Arc pH sensors can be used.

Benchtop bioreactors

Production bioreactors

Benchtop Bioreactors

Benchtop bioreactors found in laboratory and R&D cell culture applications often have fully integrated pH electronics and related calibration and configuration logic. pH sensor cables use proprietary connectors to mate with bioreactor. Examples of these connectors are shown below:

The Hamilton Arc ECS pH/ORP Adapter is a perfect tool to work with benchtop bioreactors. This specialized adapter cable powers Arc sensors and converts the digital pH measurement signal back to a standard millivolt output that is recognized by the bioreactor. The adapter is also fully compatible with the optional Wi 1G Bluetooth Wireless Adapter so that mobile devices running ArcAir software can be used to view, configure, and calibrate the Arc pH/ORP sensor.

Hamilton offers two versions of the Arc ECS pH/ORP Adapter.

  • Ref 243168-XX* includes a male BNC connector which is commonplace on certain models of Applikon and Eppendorf bioreactors.
  • Ref 243169-XX* has open leads to allow for addition of specialty connectors in the field or hard wiring to transmitter terminals.
* Note that "XX" equates to the power plug. 01 = EU, 02 = Switzerland, 03 = US, 04 = UK, 05 = AU/NZ

Hamilton also offers the Arc ECS pH/ORP Adapter in custom configurations with the bioreactor connector installed at the factory. Consult your local sales contact for options.

Production Bioreactors

Larger bioreactors used in pilot and production often use custom PLC (Programmable Logic Controller) in their design. The PLC requires a 4 to 20mA analog input for pH control. This input signal may come from a pre-existing pH transmitter or, in the case of Arc sensors, directly from the sensor itself.

Connecting Arc pH/ORP Sensors to the PLC

Since Arc pH/ORP sensors have both 4 - 20mA analog and Modbus digital outputs they are well suited for direct connection to PLCs. No secondary transmitter is needed. This strategy is ideal for saving cost and valuable panel space in new bioreactor designs. Wiring connection options are shown below.

4 - 20mA, 4-wire with wireless adapter

This is the most common wiring for Arc sensor 4 to 20mA connections to the PLC. The Arc pH/ORP sensor is shown with the Wi 2G Wireless Adapter. This design provides galvanic isolation of the 4 to 20mA outputs. It is the best choice for installations where wireless communication is desired.

Arc Wi 2G BT Wireless Adapter

4 - 20mA, 2-wire connection

This 2-wire connection scheme can also be used for Arc pH sensors. The illustration shows connection with with passive (non-powered) inputs. This simple connection method is less common since it does not support the addition of Wi Bluetooth wireless adapters. No galvanic isolation is needed in this wiring scheme.

Modbus Passive Input

Modbus RS485 serial communication

All Arc pH sensors have Modbus RS485 digital communication as a standard feature. Power and signal are kept separate in these installations. Modbus does require some additional programming at the PLC thus the Hamilton programmers manual should be consulted.

Arc pH Programmers Manual Arc ORP Programmers Manual

Connecting Arc pH/ORP Sensors to Transmitters

Most pH transmitters are designed around traditional sensors thus require a millivolt input signal. While less common, the Arc ECS pH/ORP Adapter described above can also be used to connect Arc sensors to a pre-existing transmitter. The user still benefits by using offline calibration and the advanced diagnostics and reporting capabilities of Arc sensor technology. Since most transmitters use terminal strip wiring, Ref 243169-XX is the best choice. The power supply and electronics enclosure of the adapter should be enclosed in the same panel or cabinet used for the transmitter. Temperature compensation of the pH measurement should be set to manual at 25°C to avoid errors since this compensation is already performed within the Arc electronics.

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