Temperature control has a dirty secret: the cheap thermostat holds a degree on a good day and swings five on a bad one. When the process cares — injection molds, seal bars, ovens, greenhouses — a dedicated controller costs real money, and a big PLC is overkill. The middle path is a compact PLC with a built-in PID loop, and it holds ±1°C without breaking a sweat.
The Application
Picture a small process that needs closed-loop heating: an oven chamber, a hot runner, a lab bath, a food line. A sensor measures the temperature, a heater adds energy, and something has to decide how much. The relay-based approach bangs the heater on and off and lives with the overshoot. The PID approach measures the error, the rate of change, and the accumulated offset, then drives the heater proportionally — smooth, stable, reapeatable.
The Solution: PR-18DC-DA-R
The PR-18DC-DA-R carries an 18-point CPU with a built-in PID block and floating-point math. A PT100 or 0-10V temperature signal enters the analog input, the PID block computes the output, and the relay drives an SSR feeding the heater. Setpoint and live value sit on the 4-line LCD — the operator reads the process without a screen or a PC.
What makes it stable is the math: the PID runs at the controller's scan speed, not at the 1-second tick of a cheap thermostat. In our bench test with a 1 kW heater and a PT100 sensor, the PR-18DC-DA-R held a 60°C setpoint within ±1°C after a short warm-up — and kept it there over a two-hour soak, through load changes and a 10°C ambient swing.
Want the temperture history? The same CPU reports over Modbus to EasySCADA, or to any HMI, so the quality log writes itself. On a 4G model the same loop can send an alarm if the process drifts out of band — a cold oven at 6 AM is a phone call, not a ruined batch.
What You Gain
- ±1°C stability with the built-in PID — no separate temperature controller to buy
- One CPU, many jobs: the same PLC that runs the PID can run the conveyor interlocks, the timers and the alarm
- Data for free: Modbus reporting means the temperature log exists without extra hardware
Recommended Models for Temperature Control
| Model | Best for |
| PR-18DC-DA-R | Local PID control with LCD, analog input, relay output |
| PR-23DC-PTDAI-RT-4G | PT100-ready inputs plus 4G remote alarms for unattended sites |
| PR-E-PT100/PT1000 | Add extra PT100 channels to any PR CPU when multiple zones need control |
Related: PT100 and 0-20mA inputs explained · FAQ .html">PID FAQ · Selection Guide
