Rex-C100 Temperature Controller

Temperature controllers are used to maintain a constant temperature in an environment. This includes processes, plants or even materials. There are multiple types of temperature controllers such as on-off and PID. In this article, we’ll be discussing REX-C100 series PID temperature controllers manufactured by RKC Instruments.

What is Rex-C100 Temperature Controller?

In the field of industrial automation, we often find many types of electronic controllers. One such controller type is temperature controllers. They are used to maintain a constant process temperature regardless of external disturbances.

Among the types of temperature controllers, PID controllers are the fastest and most accurate type of controllers. They use closed loop feedback systems to loosely monitor the current temperature and make adjustments when necessary.

One such PID temperature controller is the REX-C100 controller. It has a dual-line seven segment display. The top line displays the current temperature, which is also known as Process Variable (PV).  The bottom line displays the target temperature or Set Variable (SV).

The REX-C100 controller is a standard, panel-mount type PID temperature controller that is available in multiple different combinations. It is a part of the REX-Cxx series PID temperature controllers. There are 5 main types of Cxx series controllers: C900, C700, C400, C410 and C100. C100 is the one that has the smallest footprint.

C100 controllers are easy to install and follow industrial hardware footprints such as standard mounting sizes and wiring nomenclature. They can be powered from 100-240VAC or 24VAC/DC power supplies depending on the configuration.

The Cxx series controllers are based on a microcontroller that has advanced features such as automatic PID tuning. Automatic PID tuning makes tuning the proportional, integral and derivative constants an easy task.

The signal input to the device can be a thermocouple (compatible with type K, J, R, S, B, E, T, N, PLII, W5Re/W26Re, U, L)

In addition to the regular PID control, the REX-C100 PID temperature controller can be configured to work as a regular on-off, P or PI controller. It is also available in different output modes. For example, it can support either relay output, voltage pulse for SSR control, a current output (4-20mA) or even phase angle controlled pulse for direct thyristor control.

REX-C100 datasheet

The REX-C100 PID temperature controller is a device of the Cxx series temperature controllers manufactured by RKC Instruments Inc., Japan. They are a world-renowned brand for industrial automation equipment manufacturing.

Let’s have an in-depth look at the REX-C100 temperature controller’s datasheet. You can also download the datasheet from the manufacturer’s website for future reference.

Model Identification

There are multiple combinations of REX-Cxx series devices that are available to purchase. Their model numbers are selected according to the features and configurations they have.

For example, the C100 series that offer SSR control output, K-type thermocouple input that can measure temperatures from 0°C-400°C in the panel mount 48×48 package has a model name REX-C100FK02-V*EN. This also indicates that there is a deviation upper limit alarm and nos second alarm. The letter ‘F’ indicates that the device supports intelligent PID self-tuning.

REX-C100 terminal configuration and I/O

The REX series controllers can be powered by either 100-240V AC, 24VDC or 24VDC/AC power sources. The following figure shows the generic terminal configuration of REX-C100 PID temperature controller. The combinations depend on the model and configurations offered.

C100 controller supports multiple configurations of input and output types. For measuring the process temperature parameter (Process Value – PV), it can use a K. J, S type thermocouple or a PT100 resistance-temperature detector (RTD) sensor. C100 has 5 variants for different temperature ranges. In its model number, the two digit ID indicates the following:

  • 02– 0°C-400°C
  • 05– 0°C-999°C
  • 06– 0°C-1200C
  • 07– 0°C-1372°C
  • 08– 0°C-1600°C

As for the output types, C100 has 4 output types. The type is indicated in the following forms:

  • M – Relay contact output
    • A normally open relay contact output that can be used to drive a high current relay/contactor to turn on/off a heating element. This is useful when the device is configured in on/off mode.
  • V – Voltage pulse output
    • An active-high pulse output mode that can be used to control a SSR. SSR (Solid State Relay) is a semiconductor device used to control the average power applied to the heating element to regulate temperature.
  • 8 – Current output
    • A 4-20mA DC current output proportional to the PID loop output for external use
  • G – Phase shifted pulse
    • This signal can be used to control thyristors for high power control. This is most useful in systems where power electronics circuitry is custom-built and SSRs are not used.

REX-C100 display panel

The unit has a typical yet intuitive front panel which is easy to read and control. There are two digital displays in red and green colors. The top, red color display indicates the measured value (PV). PV is the current temperature of the process measured through the temperature sensor. The bottom display is a green color and displays the set point/set value (SV). This is the target temperature the device tries to maintain.

In addition to the main displays, there are 4 LED indicator lamps to indicate the status of alarms, tuning status and the control output status. Alarm output lamps are red and the autotuning lamp flashes green when tuning. Control output lamps are bi-color (green and yellow).

There are four buttons (set, shift, down and up) for navigating through menus and adjusting configurations.

How to use a REX-C100 temperature controller with SSR and thermocouple

Let’s discuss how a REX-C100 can be wired with an SSR to control temperature. The figure shown below has the following configuration:

  • 100-240VAC powered
  • SSR output
  • K-type thermocouple input type
  • Alarm output for deviation/process indication

Connect the AC supply to pin 1 and 2. To supply power to the alarm relay, connect the live connection to pin 7 as well. In the given configuration, pin 4 and 5 are used to activate the SSR

The heating pipe/heater is connected in series through a solid-state relay (SSR). The output configuration of the chosen C100 controller is voltage pulse type to control the SSR. This is a pulse that rapidly turns on/off the SSR to control the average power supplied to the heating pipe.

For measuring the process value, the thermocouple is attached to pin 9 and 10. If a PT100 type is selected, use pins 8, 9 and 10 for connections. If a PT100 is being used, make sure the red connector is connected to terminal 8 of REX-C100. The remaining two blue connectors are interchangeable and should be connected to pin 9 and 10.

REX-C100 quick initial setup

Before powering up the system, always double check and ensure that all the connections are correctly done. The REX-C100 temperature controller is a sensitive device and can get instantly damaged if sensor input lines and power input lines are connected in a wrong way.

Initial Setting

When powered on for the first time, the controller immediately asks for the input type and input temperature range. Select the correct sensor type from the table and use up/down and shift keys to adjust the settings according to the table shown below.

Press the set button once to confirm. As soon as the input type has been confirmed, the device will ask for the temperature range. In this screen, the PV display shows the upper limit and the SV display shows the lower limit for the temperature.

The main procedure to follow after turning on the power for the first time is to initialize the device. This can be done by long pressing the SET key for 5 seconds. When the unit is in parameter setting mode, the display will show ‘LCK’ as shown below:


Press the shift button to move the cursor blinking in the bottom display below the character C on the top display. Then press down key once to set the digit to 0 as shown below.

Pressing the set button again stores the set value and unlocks the initialization mode. Press and hold shift key while pressing the set key to enter and exit from the initialization mode at any time. The figure below shows the settings that are available in the initialization mode. Pressing set button cycles between the modes. Use shift key and up/down keys to adjust values in a particular mode.

In this mode, any parameter can be changed by the user without having to unlock the device. While unlocked (LCK mode shows 0000), any parameter can be changed. A value of 0101 indicates that all parameters are locked and 0110 means that only set value can be changed.

Changing operating parameters

The set value is the most frequently changed value. This is the target temperature the temperature controller tries to maintain. The device follows the following sequence upon powering on.

To change the set value, press the set button at the SV/PV monitor screen until SV setting is displayed. In this mode, using the shift key, the cursor can be moved left right and up/down keys can be used to increase/decrease the corresponding digits. After setting the value, press the set key to confirm and save the set value.

How to solve REX-C100 temperature controller not working

Temperature controllers can sometimes malfunction or cease to work at all due to many possible reasons.

Smart controllers such as REX-C100 temperature controllers offer some type of error display methods to indicate a problem. This is usually done through error codes and helps the technicians troubleshoot the problem faster. As a precaution, make sure to power down the system before attempting any electrical changes to prevent electric shock.

Here are some common errors in REX-C100 and how to solve them:

  • PV value is not updating
    • Check sensor wiring and make sure the connectors are properly tightened.
  • Load is not turning on
    • Check if the output LED is flashing when the system temperature changes. If so, check the SSR or any other control element if not faulty.
  • PV value is flashing
    • This indicates that the PV value is outside the range. Check the PV range and temperature sensor connections.
  • Flashing ‘oooo’ text in PV display
    • This indicates that the PV value measured is higher than the specified range. Check the sensor connections and verify the PV range upper limit.
  • Flashing ‘uuuu’
    • This indicates that the PV value measured is lower than the specified range. Check the sensor connections and verify the PV range lower limit
  • Display indicated ‘ERR’
    • If this text is displayed, the power should immediately be turned off. Try restarting the unit by turning it back on. If the message does not clear, the unit’s memory is corrupted and should be serviced by authorized personnel.


In this article, we discussed the REX-C100 PID temperature controller, its features, applications and how to troubleshoot some of the most common issues. For more information on the device and how to configure the additional settings, refer to the user manual of REX-C100.

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