Piketronic RPP-R Radon Probe
Description
The Piketronic RPP-R is a radon probe that continuously measures radon concentration along with the air temperature and humidity inside its measurement chamber. It is equipped with an RS-485 Modbus RTU interface for reading the measured values. This device is supported by the CHESTER Serial application.
The radon probe is a self-contained sensor — it does not require any external sensor. A new radon concentration value becomes available every 4 minutes; reading more frequently returns the same value.
Modbus Communication
Example of Modbus Communication Installation: Piketronic RPP-R
The RPP-R has a 4-pin connector labelled B RxTx-, A RxTx+, GND, VCC.
| Piketronic RPP-R | CHESTER Modbus |
|---|---|
| A RxTx+ | Pin 7 (A) |
| B RxTx- | Pin 6 (B) |
| GND | Pin 1 (GND) |
| VCC | Power (see note below) |
The probe needs a supply on VCC. It can be powered from CHESTER's dedicated power output (VIN) if the voltage and current match the RPP-R's requirement — confirm the probe's supply voltage first; otherwise use a separate external supply. RS-485 A/B labelling varies between manufacturers; if no data is received, swap the A and B lines.
Browsing and Configuration
The RPP-R has no display or buttons. Its Modbus address and serial parameters are set with two DIP-switch blocks on the probe. The probe must be restarted (power-cycled) after changing any switch.
Address (switch block ADDRESS)
A value from 1 to 247. Switch labelled 1 is the least significant bit; a
switch in the down position means logical 0.
Speed and parity (switch block RATE, switches 4-3-2-1)
| RATE (4 3 2 1) | Baud Rate | Parity | Stop Bit |
|---|---|---|---|
| 0 0 0 0 | 19.2k | Even | 1 |
| 0 0 0 1 | 9.6k | Even | 1 |
| 0 0 1 0 | 2.4k | Even | 1 |
| 0 0 1 1 | 1.2k | Even | 1 |
| 0 1 0 0 | 19.2k | Odd | 1 |
| 0 1 0 1 | 9.6k | Odd | 1 |
| 0 1 1 0 | 2.4k | Odd | 1 |
| 0 1 1 1 | 1.2k | Odd | 1 |
| 1 0 0 0 | 19.2k | None | 2 |
| 1 0 0 1 | 9.6k | None | 2 |
| 1 0 1 0 | 2.4k | None | 2 |
| 1 0 1 1 | 1.2k | None | 2 |
| 1 1 x x | do not use |
Default Modbus Communication Configuration
| Address | Baud Rate | Parity | Stop Bit |
|---|---|---|---|
| 1 | 19.2k | Even | 1 |
The table above is the recommended setup (RATE switches all down). Always set
CHESTER to match the switches actually configured on the probe.
Modbus Communication Configuration for Chester
Use the following commands to configure the CHESTER Serial application via the
Chester terminal. The probe is added as a Modbus device of type piketronic.
app config serial-mode "modbus"
app config serial-baudrate "19200"
app config serial-parity "even"
app config serial-stop-bits "1"
app config device-0 "piketronic,1"
config save
The device-0 value is type,address — here type piketronic at Modbus address 1.
You can also read the probe directly from the terminal at any time:
device piketronic sample 1
This prints the radon concentration (1-hour and 1-day average), temperature, humidity, current settings, and the probe's device/firmware/serial identification.
Measured values
Decoder: com.hardwario.chester.app.serial — values appear under the devices
array (devices → data).
| Measured Value | Key / Path | Unit |
|---|---|---|
| Radon concentration (1 h) | devices → data → radon_concentration | Bq/m³ |
| Radon concentration (1 day) | devices → data → radon_concentration_day | Bq/m³ |
| Temperature | devices → data → temperature | °C |
| Humidity | devices → data → humidity | % |
The radon concentration is a 1-hour moving average (updated every 4 minutes). A separate 1-day moving average is also reported.