Remote terminal units · I/O count and types, analog accuracy across temperature, sampling and timestamps, event pre-recording, isolation and surge, communications, power, hazardous-area and rail approvals
A remote terminal unit (RTU) is a rugged microprocessor controller, with digital and analog input/output channels, serial and network communications and a wide-range DC power supply in a DIN-rail housing, that collects measurements and states from field equipment at remote sites, runs local logic and reports to SCADA or cloud systems. Ask three things first: how many and which inputs and outputs it needs and how accurate the analog channels must be across the site's temperatures, which communication links and protocols it must use, and what power, isolation and approvals the site requires.
Remote terminal units and programmable RTU controllers for utilities, water, oil and gas, rail and environmental monitoring. General-purpose PLCs, protocol gateways without I/O, data loggers without control and cellular routers are outside this page.
01
Moxa's ioPAC 5542 data sheet lists 8 digital inputs (wet NPN/PNP or dry contact, with counter and frequency modes to 1 kHz), 8 configurable digital I/O (sink outputs, 200 mA per channel, with PWM) and 8 differential analog inputs of 16-bit resolution for 0–10 V, ±10 V, 0–20 mA or 4–20 mA, isolated at 3 kV DC or 2 kV rms. Analog accuracy is ±0.1% of full-scale range at 25 °C and ±0.3% at −40 and 75 °C; sampling reaches 250 samples per second per channel (2,000 for all channels), with millisecond timestamps on digital and analog inputs. [1]
Its prerecord function records analog data continuously before an event trigger, with a 60 KB buffer per channel holding 120 seconds at 250 Hz, so the build-up to an event is not lost while logging starts. It is programmable in C/C++ or IEC 61131-3. [1]
Editorial calculation: on a 4–20 mA pressure transmitter spanning 0–10 bar, ±0.1% of a 20 mA full-scale range is ±0.02 mA, or about ±0.0125 bar (10 bar ÷ 16 mA); at −40 or 75 °C, ±0.3% triples that to about ±0.04 bar, before adding the transmitter's own error. Specify accuracy at the site's temperature extremes, not at 25 °C. [1]
Give the supplier the number and type of digital inputs, digital outputs, analog inputs (signal ranges) and analog outputs, required accuracy across the temperature range, sampling and timestamp needs, event logging, control logic and programming language, communications (Ethernet, serial, cellular, radio) and protocols (Modbus, DNP3, IEC 60870-5-104), supply voltage, temperature range, approvals (hazardous area, rail), mounting and quantities.
02
The ioPAC 5542 has two 10/100 Mbps Ethernet ports with 1.5 kV magnetic isolation, two software-selectable RS-232/422/485 serial ports with 15 kV ESD protection and an optional HSPA cellular version; its listed protocols include Modbus TCP/RTU master and slave, SNMP, SNTP and SMTP. It takes 24 V DC (9–48 V) at 264 mA (305 mA for the cellular model) and operates from −40 to 75 °C (−30 to 75 °C cellular) up to 2,000 m. [1]
Surge immunity is 2 kV line-to-earth and 1 kV line-to-line on power and 1 kV on signal lines to IEC 61000-4-5, with shock and vibration tested to IEC 60068-2-27 and -2-6. Approvals include UL 508, EN 50121-4 for rail and Class I Division 2 for hazardous locations; the aluminium housing weighs 1,000 g (1,100 g cellular) and carries a five-year warranty. [1]
Editorial calculation: 264 mA at 24 V is about 6.3 W; a solar or battery-powered site would need roughly 6.3 × 24 ≈ 152 Wh per day for the RTU alone, before radios and sensors. [1]
03
IEEE 1815-2012 specifies the DNP3 protocol structure, functions and interoperable subset levels, from the simplest level for low-cost distribution feeder devices up to full-featured systems, with the level chosen to suit each device; it runs on a variety of communication media. IEEE lists the 2012 edition as inactive-reserved since 30 March 2023, so ask suppliers which edition and subset level their DNP3 implementation conforms to. [2]
IEC 60870-5-104 (2006, consolidated with Amendment 1 of 2016) is the telecontrol companion standard that carries IEC 60870-5-101 over standard network transport profiles, for monitoring and controlling geographically widespread processes with coded bit-serial data, so that compatible telecontrol equipment interoperates. [3]
Editorial note: protocol names alone do not guarantee interoperability with your SCADA master; ask for the DNP3 device profile or the IEC 60870-5-104 interoperability list for the RTU, and test them against the master before roll-out. [2] [3]
04
Suppliers linked to this page list remote terminal units; each card links to the page reviewed.
Listings include RTUs for hydrology and environmental monitoring, power-distribution RTUs, gateway-RTU combinations and RTUs paired with radar level and flow meters.
05
Schneider Electric's SCADAPack 470/474 data sheet (December 2022) lists DNP3 level 4 with Secure Authentication and IEC 60870-5-104 as a controlled station, alongside Modbus RTU and Modbus/TCP, with built-in protocol analysers for DNP3, IEC 60870-5-104 and Modbus. On the 474, analog inputs 1–4 are 12-bit and non-isolated, while inputs 5–12 are 24-bit and isolated from logic and chassis, sampled in 100 ms for all 8 channels without filtering or 500 ms with the 50/60 Hz filter; relay outputs are Form A, 2 A at 30 V DC. [4]
Rated input is 14–29 V DC. Operating temperature is −40 to 70 °C when the unit is mounted horizontally on a vertical surface, but −40 to 65 °C in any other position. The internal file system stores up to 1,000,000 events, and a USB drive or microSD card up to 100,000,000. Class I, Division 2 and Zone 2 hazardous area certifications are included. [4]
Editorial calculation: the 474's 4 W is 4 × 24 = 96 Wh per day, against about 152 Wh for the ioPAC 5542 above. The 474 loses 5 °C of rating (70 − 65) away from its preferred orientation, so state mounting orientation and enclosure temperature in the enquiry. [4] [1]
06
This is a functional reference built from the sources cited; it is not one maker's design.
| Part | Role | Fix in the order |
|---|---|---|
| Main CPU and memory | Logic and communications. [1] | CPU, memory, storage. |
| I/O processor | Sampling and timestamps. [1] | Rates and resolution. |
| Digital and analog I/O | Field signals. [1] | Counts, ranges, isolation. |
| Communication ports | Ethernet, serial, cellular. [1] | Ports and protocols. |
| Power input | DC supply. [1] | Range and current. |
| Housing | Ruggedness and approvals. [1] | Material, approvals. |
07
An RTU quotation needs values for your site. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Operating Temperature (°C) | −40 to 75 °C in one model. [1] | Range and variants. |
| Supply Voltage (V DC) | 9–48 V DC. [1] | Range. |
| Power Consumption (W) | 264 mA at 24 V (≈ 6.3 W). [1] | Power with comms. |
| Analog Input Channels (channels) | 8 differential, 16-bit. [1] | Channels and ranges. |
| Digital Input Channels (channels) | 8 plus 8 configurable. [1] | Channels and types. |
| Analog Output Channels (channels) | Not on the model reviewed. | Channels if needed. |
| Digital Output Channels (channels) | Up to 8 sink outputs, 200 mA each. [1] | Channels and rating. |
| Analog Input Accuracy (% FS) | ±0.1% at 25 °C; ±0.3% at −40/75 °C. [1] | Accuracy over temperature. |
| Communication Protocol | Modbus TCP/RTU, SNMP and others. [1] | Protocols incl. DNP3/IEC 104. |
| Ingress Protection | Cabinet mounting. | IP code. |
| Humidity (% RH) | 5–95% non-condensing. [1] | Range. |
| Dimensions (W x H x D) (mm) | 90.05 × 135 × 105.4 mm. [1] | Drawing. |
| Weight (kg) | 1.0–1.1 kg. [1] | Weight. |
08
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
I/O: [DI; DO; AI ranges; AO] Accuracy: [% FS at temperature extremes] Timing: [sampling; timestamps; event logging] Comms: [Ethernet; serial; cellular; protocols] Site: [DC supply; temperature; approvals] Supply: [programming; mounting; quantity]
These companies list remote terminal units.
Lists remote terminal units (M21F series) alongside BeiDou terminals and IoT data loggers.
Product scope checked 2026-10-11
Lists gateways and remote terminal units among industrial automation products.
Product scope checked 2026-10-11
Lists a remote terminal unit among power monitoring products.
Product scope checked 2026-10-11
Lists the H1951 remote terminal unit alongside radar level and flow meters.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Moxa's ioPAC 5542 lists ±0.1% of full-scale range at 25 °C and ±0.3% at −40 and 75 °C. [1]
The ioPAC 5542's prerecord function keeps up to 120 seconds of analog data at 250 Hz before a trigger. [1]
The ioPAC 5542 is approved for Class I Division 2, and for rail use to EN 50121-4. [1]
DNP3 (IEEE 1815) and IEC 60870-5-104, which carries IEC 60870-5-101 telecontrol messages over network transport. [2] [3]
In Schneider Electric's SCADAPack 470/474 data sheet it does: −40 to 70 °C mounted horizontally on a vertical surface, −40 to 65 °C in any other position. [4]
Sources checked 2026-10-12. Moxa publishes the data sheet for its own RTU controller; values for your RTU must come from the supplier's data sheet and certificates.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
Compare manufacturer profiles with relevant product and process capability.