Temperature Measurement in a Panel: PT100, 4-20 mA Transmitter, RS485 or PID — Which Part Do You Need?
Short answer: A temperature point in a panel is a chain of parts. A sensor touches the process (PT100 RTD or K thermocouple). A transmitter turns the reading into a signal your PLC or RTU understands (4-20 mA or RS485 Modbus). A controller acts on it (for example a PID that switches a heater). Buy only the part you are missing. The four parts below are in stock at AutomationBotX, with specs taken from their listings.
Which part do I need?
| You have… | You need… | Part | Price (USD) |
|---|---|---|---|
| A PLC analog input and no sensor yet | A PT100 probe plus a 4-20 mA transmitter | WZP-PT100 probe + DIN-rail PT100 transmitter | from $6.01 + $32.99 |
| A PT100 already installed, but the PLC only reads 4-20 mA | A PT100 transmitter | DIN-rail PT100 transmitter | $32.99 |
| An RS485 Modbus network and a room or shelter to watch | A Modbus temperature and humidity transmitter | CWT-XYTH RS485 transmitter | from $49.99 |
| An electric heater to hold at a set temperature, no PLC | A standalone PID controller with SSR and probe | PID controller kit (K thermocouple, 40 A SSR) | $43.99 |
Prices as listed on 5 November 2026; the product page always shows the current price for each variant.
The four parts, side by side
| WZP-PT100 probe | PT100 transmitter | CWT-XYTH RS485 | PID controller kit | |
|---|---|---|---|---|
| Store SKU | ABX-0634 | ABX-AE-008861 | ABX-AE-350305 | ABX-AE-952234 |
| Role | Sensor | Transmitter (PT100 in, 4-20 mA out) | Sensor + transmitter (RS485 out) | Controller + SSR + probe |
| Sensing element | PT100 RTD | Takes a PT100 input | Built-in temperature and humidity | K-type thermocouple |
| Range | -20 to 450 °C in the listing’s parameters (the same listing also states -200 to 600 °C as measurement range) | Choose a span from 0-50 °C up to 0-500 °C, or -50 to 50/100/150/200 °C | -40 to 125 °C, 0-100 % RH | 0-400 °C |
| Output | Resistance (to a transmitter or controller) | 4-20 mA | RS485 Modbus RTU (default 9600 8N1, address 1) | SSR drive to a 40 A SSR (load 24-380 VAC) |
| Supply | n/a | 24 VDC | 12-24 VDC | 100-240 VAC |
| Mounting | Ø4 x 30 mm tube, 0.5 m cable | DIN rail | Wall or 35 mm DIN rail | 48 x 96 mm panel cut-out |
Questions and answers
PT100 or K thermocouple?
Both appear above. A PT100 is a resistance sensor and needs a PT100 input or a PT100 transmitter. A K thermocouple produces a small voltage and needs a thermocouple input, like the one on the PID controller in the kit. Do not mix them: a PT100 transmitter cannot read a thermocouple.
How do I choose the transmitter range?
Pick the narrowest span that still covers your highest and lowest expected temperatures. The 4-20 mA signal is spread over that span, so a tighter span gives your PLC finer steps.
How does the PLC scale the RS485 transmitter?
Per the listing, the temperature register reads 0-1650 for -40 to 125 °C, and the humidity register reads 0-1000 for 0-100 % RH.
Can I use these in a hazardous area?
None of these listings includes a hazardous-area certificate. Mount them in a safe-area panel or shelter, and confirm what your site requires before you order.
Buy
- WZP-PT100 probe, 1 or 5 pieces, from $6.01
- DIN-rail PT100 transmitter, 4-20 mA, $32.99
- CWT-XYTH RS485 temperature and humidity transmitter, from $49.99
- PID temperature controller kit with 40 A SSR and K probe, $43.99
Free US shipping on every order. Specs above come from the product listings; if a value you need is not listed, it is not stated by the supplier.