Feedback controller: multi-loop PID controller module for DIN-rail mounting
Multi-loop feedback (PID) controller modules · loops per module, input accuracy and sampling time, 4–20 mA outputs, heater-current monitoring, fieldbus link to the PLC
A feedback controller compares a measured value with its setpoint and drives an output to close the difference. In machines and process skids with multiple temperature or process loops, this is done by a multi-loop PID controller module on a DIN rail: one unit reads multiple sensors, runs a PID loop for each, drives heater or valve outputs, and reports to the PLC or HMI over a network. Ask three things first: how many loops and inputs the machine needs, what input accuracy and sampling time each loop requires, and how the module will talk to the PLC.
DIN-rail and modular multi-loop PID controllers that run two or more independent feedback loops for temperature and process variables, specified by loops per module, input accuracy, sampling time, output type and fieldbus link. PLC-based machine control systems, with CPU, motion and I/O modules, are covered on the Industrial control systems page. Single-loop panel controllers, servo drives and position controllers are outside this page except where compared.
CNFX editorial research · Sources checked October 12, 2026 · 3 sources
Count the loops, then pick how they are packaged: 4 per module or up to 16 per unit
Eurotherm's Mini8 is one DIN-rail unit (124 × 108 × 115 mm, about 1 kg) offering 16 control loops and 32 analog inputs, ordered with 0, 4, 8, 16 or 24 loops (24 only with its SuperLoop option). Its loops run on/off, single PID or dual-channel output, with 3 PID sets, one-shot auto-tune and cascade control in SuperLoop; Eurotherm presents it as a partner to a PLC that takes analog measurement and loop control off the PLC. [1]
RKC's SRZ takes the modular route: each Z-TIO module controls 4 channels (2 when used for heat/cool control), and up to 16 modules connect together for a maximum of 64 channels, with separate digital I/O, CT input and communication modules. [2] Gefran's GFXTermo4 is a 4-loop DIN-rail unit, also mountable with two M4 screws, with 4 universal process inputs, 4 independent heat/cool PIDs, 4 main outputs, 4 auxiliary analog inputs and inputs for external current transformers. [3]
Editorial calculation: RKC's 16 modules × 4 channels gives its stated 64-channel maximum; a 24-zone machine would need 6 SRZ temperature modules or one Mini8 with the 24-loop SuperLoop option, or 6 GFXTermo4 units. Editorial note: count heat/cool zones separately, because RKC halves channels per module for heat/cool control. [2]
Give the supplier the number of loops and their type (heat only, heat/cool, process), sensor types and ranges, output type for each loop (logic to SSR, relay, 4–20 mA), heater current monitoring needed, PLC or HMI and fieldbus, supply voltage, cabinet temperature, and any furnace or pyrometry standard the loops must meet.
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Read input accuracy, sampling time and output accuracy as limits on each loop
RKC states a measurement accuracy of ±0.2% of displayed value and a sampling time of 0.25 s for the SRZ. [2] Eurotherm's Mini8 TC8 thermocouple card gives a total accuracy of ±1 °C ±0.1% of reading with internal cold-junction compensation, and its ET8 card ±0.25 °C ±0.05% of reading at 25 °C ambient, from a 20-bit sigma-delta converter; Eurotherm states that with field calibration the ET8 version suits Nadcap work in all furnace classes defined in AMS2750F. [1]
On the output side, the Mini8 AO4/AO8 cards drive 0–20 mA (used for 4–20 mA loops) into up to 360 Ω with ±0.5% of reading setting accuracy and 1 part in 10,000 resolution. [1] Editorial calculation: 20 mA into 360 Ω needs 7.2 V, so the valve positioner or power controller input plus cable resistance must stay under 360 Ω.
Heater loops can also be watched for failure: with a 3-input current transformer card, the Mini8 detects partial load failure, over-current and SSR short or open circuit on up to 8 loops. [1] For networking, GFXTermo4 uses a Modbus RTU local bus at 115 kbit/s plus a fieldbus port for Profibus DP, CANopen, DeviceNet, Modbus RTU or Modbus TCP, and the Mini8 lists Modbus RTU, DeviceNet, Modbus TCP and EtherNet/IP. [3][1]
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Three published multi-loop controllers side by side
The three differ in how loops are grouped and in what the vendor publishes about accuracy.
Item
Eurotherm Mini8
RKC SRZ
Gefran GFXTermo4
Loops
Up to 16 (24 with SuperLoop); 32 analog inputs. [1]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How many loops can one feedback controller module run?
Eurotherm's Mini8 offers up to 16 loops (24 with SuperLoop); RKC's SRZ runs 4 channels per module and up to 64 per system; Gefran's GFXTermo4 runs 4. [1][2][3]
How accurate are multi-loop controller inputs?
RKC states ±0.2% of displayed value for the SRZ; Eurotherm gives ±1 °C ±0.1% of reading for the Mini8 TC8 card and ±0.25 °C ±0.05% for the ET8 card. [2][1]
Why use a multi-loop controller beside a PLC?
Eurotherm presents the Mini8 as taking analog measurement and loop control off the PLC, which can allow a lower-specification PLC processor. [1]
Sources and what still needs a direct check
Sources checked 2026-10-12. Eurotherm, RKC and Gefran describe their own multi-loop controllers. The datasheet of the exact model and card set governs.
