4WFBS120 120-Ohm, Four-Wire Full-Bridge Terminal Input Module


The 4WFBS120 is a four-wire, full-bridge module that provides completion resistors for a strain gage or other sensor that acts as a single variable resistor. This module should be used to measure sensors that have a 120-ohm nominal resistance.

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Benefits and Features

  • Easy to install or remove
  • Connects directly into data logger input terminals
  • Compatible with most Campbell Scientific data loggers


Detailed Description

The 4WFBS120 completes a full Wheatstone bridge. It can also be used to complete the back half of a Wheatstone bridge for use in a ¼ bridge strain circuit (one active element) using a dummy gage, or in a ½ bridge strain circuit (two active elements). The Wheatstone bridge circuit converts small changes in resistance to an output voltage that our data loggers can measure.

The 4WFBS120 includes two external pins that allow customers to perform shunt calibrations, which are used to correct for sensitivity errors.

4-Wire Full Bridge Module Schematic
(R4=120 Ω for the 4WFBS120)

4WFBS120-to-Sensor Hookup


Used With 4-wire strain gages or other full bridge measurements that have a 120 Ω nominal resistance
Dimensions 1.5 x 1.5 x 2.7 cm (0.6 x 0.6 x 1.0 in.) for body with prongs
Weight 6 g (0.2 oz)

2:1 Resistive Divider

Resistance 1 kΩ/1 kΩ
Tolerance Ratio: ±0.01% (@ 25°C)
Maximum Temperature Coefficient Ratio: 0.5 ppm/°C (-55° to +85°C)
Power Rating 0.1 W (@ 70°C) per element

Completion Resistor (bulk metal foil)

Resistance 120 Ω
Tolerance ±0.01% (@ 25°C)
Maximum Temperature Coefficient 0.8 ppm/°C
Power Rating 0.25 W (@ 70°C)


Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Data Loggers

Product Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR23X (retired)
CR295X (retired)
CR3000 (retired)
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR800 (retired)
CR850 (retired)


Product Compatible Note
CR9050 (retired)

Additional Compatibility Information


The 4WFBS120 is compatible with our multiplexers.

Data Logger Considerations

The 4WFBS120 uses one differential analog input; an adjacent analog ground channel accepts the "ground prong" of the 4WFBS120. Not all data logger terminal strips have this sequence on all channels, so please check your data logger's wiring panel to confirm channel assignments, especially if you plan to use multiple Terminal Input Modules.

The lead wire that emanates from the head of the 4WFBS120 connects to a data logger excitation channel.

Please note that if a CR10X will be used to measure thermocouples in the same application, newer CR10X Wiring Panels and the CR10XTCR Reference Thermistor (with its accompanying Thermocouple Cover) are deep enough to cover the data logger input channels with a Terminal Input Module attached; older CR10TCRs are not deep enough.


The 4WFBS120 is measured with the BrFull Instruction in CRBasic, and with Instruction 6 (Full Bridge) in Edlog.

Frequently Asked Questions

Number of FAQs related to 4WFBS120: 5

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  1. The CR1000 excitation channel current limit is 25 mA at 2500 mV. Using 120 ohm gages with multiple 4WFBS120 modules, only two gages can be hooked up for each excitation channel with 2500 mV excitation. If three gages per excitation channel are used, the excitation needs to be reduced to approximately 1750 mV.

  2. The ST350 is designed as a full-bridge strain transducer with four active elements that can be directly connected to a data logger (or a multiplexer connected to a data logger) without adding a completion module such as the 4WFBS350 or 4WFBS120.

  3. Each data logger has specific excitation current sourcing capability. It is imperative not to exceed this current limit when trying to excite multiple strain gages from the same excitation channel.

    • The equivalent resistance of the 4WFBS120 is 214.285 ohm. If the circuit is being excited with 2.5 V (2500 mV), it will draw 11.67 mA (2500 mV / 214.285 ohm = 11.67 mA).
    • The equivalent resistance of the 4WFBS350 is 518.518 ohm. If the circuit is being excited with 2.5 V (2500 mV), it will draw 4.82 mA (2500 mV / 518.518 ohm = 4.82 mA).
    • The equivalent resistance of the 4WFBS1K is 1000.00 ohm. If the circuit is being excited with 2.5 V (2500 mV), it will draw 2.5 mA (2500 mV / 1000 ohm = 2.5 mA).
  4. More than one strain gage sensor can use the same excitation terminal if the bridge resistance is high enough or the excitation voltage is limited. The limit is determined by the current capacity of the excitation terminal (25 mA at 2.5 V) and the equivalent resistance of the circuit.

  5. To make strain gage measurements, a terminal input module is needed. It is necessary to match the resistance of the strain gage with the resistance of the terminal input module.

    • For a 120 ohm strain gage, use the 4WFBS120.
    • For a 350 ohm strain gage, use the 4WFBS350.
    • For a 1000 ohm (1 kohm) strain gage, use the 4WFBS1K.

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