RS485 Modbus to Ethernet, WiFi, Cellular or LoRa: Getting 4-20 mA Field Signals Off the Panel (USR-DR134, USR-W610, USR-MB706, E90-DTU)
Short answer: to get a 4-20 mA or 0-10 V field signal off a panel, first put it on an RS485 Modbus RTU bus (an analog I/O module, isolated with a signal isolator if needed). Then pick the link by distance and site: serial-to-Ethernet if a network cable reaches the panel, WiFi for short hops inside a plant, LTE Cat-M1 cellular for a remote site with carrier coverage, or a 900 MHz LoRa radio pair for point-to-point links where there is no network at all. Find it by part number. Buy it with the specs in front of you.
Step 1: get the analog signal onto Modbus RTU
- Analog I/O module: the 4AI-4DI-4DO Modbus RTU module reads 4 x 4-20 mA (R4DIK04) or 4 x 0-10 V (R4DVI041) inputs plus 4 opto-isolated NPN digital inputs, and has 4 relay outputs rated 10 A. It answers Modbus function codes 01-06, 15 and 16; up to 64 devices share one RS485 bus; 9600 bps by default (1200-115200 selectable). 12 or 24 VDC supply.
- Signal isolator / converter: if the transmitter and the module do not share a ground, or one signal must feed two devices, put a DIN-rail 4-20 mA isolator in between. It takes 4-20 mA, 0-20 mA, 0-5 V or 0-10 V in, gives the same ranges out, and comes as 1 in / 1-4 out or 2 in / 2 out (24 VDC). State the input and output ranges in the order notes.
- Already have an RS485 sensor? Many transmitters (temperature/humidity, dissolved oxygen, pH) speak Modbus RTU directly and can go straight to Step 2.
Step 2: Specs at a glance — RS485 links
| Product | Link | Serial ports | Protocols (as listed) | Supply / mounting | Price |
|---|---|---|---|---|---|
| PUSR USR-DR134 / DR132 | Ethernet (wired) | RS485 (DR134) or RS232 (DR132) | Modbus RTU to TCP, HTTP, MQTT, edge computing | 5-24 VDC, DIN rail | $43.99 |
| PUSR USR-W610 | WiFi 802.11 b/g/n + 2 Ethernet ports | RS232 and RS485 | TCP, UDP, HTTP, MQTT, Modbus gateway; up to 1000 edge data points | DC input, wall/panel ears | $67.99 |
| USR-MB706 | Cellular LTE Cat-M1 / Cat-NB2 / EGPRS | RS232, RS485 | Transparent, HTTP, SMS, FTP; Modbus support | 9-36 V | $154.99 |
| CDEBYTE E90-DTU-SL | LoRa radio, 900 MHz band (needs one unit at each end) | RS232 / RS485 | Transparent serial link; LBT, RSSI; 0.3-62.5 kbps air rate | Supply not listed — check the manual; -40 to +85 °C | $69.99 – $117.99 (22 / 30 / 33 dBm) |
Which link fits my site?
| Situation | Look at | Why |
|---|---|---|
| Panel already has a network cable or switch nearby; SCADA or HMI on the plant LAN | USR-DR134 | Wired, DIN-rail, lowest cost per point; Modbus RTU to TCP |
| Building or plant with WiFi coverage, no cable to the panel | USR-W610 | WiFi client or access point plus two Ethernet ports; MQTT and edge data points |
| Remote tank, pump station or well site with carrier coverage and no network | USR-MB706 | LTE Cat-M1 / NB2 from a 9-36 V supply (needs a SIM and data plan that supports Cat-M1) |
| Two points on a lease or yard with no cable and no cellular service | E90-DTU-SL pair | License-free 900 MHz band, no monthly data plan; range depends on power, antenna, height and terrain |
Frequently asked questions
What is the difference between Modbus RTU and Modbus TCP?
Modbus RTU runs over a serial line (usually RS485); Modbus TCP runs over Ethernet. A serial-to-Ethernet converter such as the USR-DR134 lets a Modbus TCP master on the network read Modbus RTU devices on the RS485 bus.
How many devices can I put on one RS485 bus?
The 4AI-4DI-4DO module listing allows up to 64 devices in parallel. Give each one a unique Modbus address and the same baud rate (9600 bps by default on that module).
Do I need a signal isolator?
Use one when the transmitter and the receiving input are powered from different supplies or grounds, when one 4-20 mA signal must feed two devices, or when you need to convert current to voltage (or the reverse). The DIN-rail isolator above offers up to 4 outputs from one input.
How far does the LoRa radio reach?
The supplier gives up to 10 km for the E90-DTU series, but real range depends on transmit power (22, 30 or 33 dBm), antenna, mounting height and terrain. The listing has no radio certification documents; the buyer is responsible for using the band and power allowed where it is installed.
Does the cellular DTU include a SIM card or data plan?
The USR-MB706 listing does not mention a SIM or data plan, so plan on supplying a SIM from a carrier that supports LTE Cat-M1 or NB-IoT at the site.
Can I use these links to control equipment or for shutdowns?
The 4AI-4DI-4DO module has relay outputs, but none of these links has a safety rating. Do not use them for safety shutdowns or for control of hazardous processes, and the listings state no hazardous-area rating: install them in non-classified areas or in an enclosure your site approves.
Can I see the readings on my phone?
Yes, for monitoring. Once the signal is on Modbus, a gateway can send it to AutomationBotX Cloud: live values, trend charts and alarm rules in the app. It is read-only monitoring: it never sends commands to your equipment and it is not a safety system. The first 10 machines are free, no card needed. How the signal gets from the sensor to your phone.
Need several units?
Ask for a written volume quote on our wholesale page. More field equipment: oil and gas automation.
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. Prices checked on November 12, 2026 and may change; the product page shows the current price.