EM410-RDL vs EM411-RDL: the difference is ATEX certification

Short answer: The measurement is the same on both. Same 60 GHz millimetre wave radar, same 0.3 m to 12 m range, same 8° beam, same 1 mm resolution, same accuracy up to plus or minus 2 mm, same IP68 PVDF body, same 19000 mAh cell. The EM411-RDL adds ATEX Zone 0 certification, and that is what you are paying the difference for. If your installation is not in a hazardous area, the EM410-RDL is the same instrument for less.

When you need the ATEX unit

ATEX Zone 0 means a place where an explosive gas atmosphere is present continuously, or for long periods. In practice that is the inside of a fuel or solvent tank, sealed vessels holding volatile liquids, and parts of wastewater and digester installations where gas accumulates.

This is a legal and insurance question, not a preference. If the area is classified, a non-certified sensor is not permitted in it whatever its IP rating, and no amount of enclosure fixes that. If you are unsure whether your installation is classified, the person who holds the DSEAR assessment for the site will know, and that is the question to ask before ordering either unit.

Conversely, if you are measuring a water reservoir, a river, a storm tank, a grain silo or a sewer with no classification, the ATEX certification buys you nothing. That is most level monitoring, and the EM410-RDL is the correct choice for it.

The EM410-RDL is the tougher one on temperature

Worth noticing, because it runs against the usual assumption that the more expensive certified model is more capable across the board. The EM410-RDL LoRaWAN version is rated -40°C to +70°C. The EM411-RDL is rated -20°C to +60°C.

Intrinsic safety certification constrains the design, and a narrower thermal window is part of that. For an exposed UK outdoor installation -20°C is unlikely to be the binding limit, but for a cold store, a chilled process or a hot vessel it might be, and it is the kind of thing that only becomes obvious after commissioning.

One other difference: the thread

The EM410-RDL supports a G1½” tank thread. The EM411-RDL supports G1½” or NPT1½” as a hardware option. If you are fitting into an existing NPT boss, only the EM411-RDL offers it, so on a retrofit the thread can decide this even outside a hazardous area.

Why radar rather than ultrasonic

Both of these are non-contact and read through the conditions that defeat an ultrasonic sensor: dust, steam, condensate, foam, temperature layering and acoustic noise. Nothing touches the medium, so there is no fouling and no corrosion path, which is why radar is the usual answer for sewage, slurry, chemicals and anything with a crust or a vapour layer. Both give a radar-echo curve and a diagnostic function, so a bad reading can be investigated rather than guessed at, and both store 2,000 entries with retransmission.

Where the medium is clean water in a quiet tank and there is no hazardous classification, the cheaper ultrasonic EM400-UDL will often do the same job for a fraction of the price. Radar earns its cost in difficult media, not in easy ones.

Frequently asked questions

What is the actual difference between the EM410-RDL and EM411-RDL?

ATEX Zone 0 certification, plus the tank thread options. The radar itself is identical: 60 GHz millimetre wave, 0.3 m to 12 m, 8 degree beam, 1 mm resolution, accuracy up to plus or minus 2 mm, IP68 PVDF housing, one 19000 mAh ER34615 cell. The EM411-RDL is certified for ATEX Zone 0 and offers G1.5 inch or NPT1.5 inch threads; the EM410-RDL is CE and FCC with G1.5 inch only.

Do I need the ATEX version?

Only if the installation is in a classified hazardous area, which is a legal question rather than a preference. ATEX Zone 0 covers places where an explosive gas atmosphere is present continuously or for long periods, such as inside fuel and solvent tanks or parts of digester installations. The site's DSEAR assessment defines this. For reservoirs, rivers, storm tanks, silos and unclassified sewers, the EM410-RDL is the right choice.

Which has the wider operating temperature range?

The EM410-RDL, at -40 degC to +70 degC for the LoRaWAN version, against -20 degC to +60 degC for the EM411-RDL. That runs against the usual assumption that the certified model is more capable everywhere: intrinsic safety certification constrains the design. For a cold store or a hot vessel, check this before assuming the ATEX unit is the tougher one.

Should I use radar or ultrasonic for level measurement?

Radar where the medium is difficult: dust, steam, condensate, foam, crusting, temperature layering or acoustic noise, all of which degrade an ultrasonic reading. Radar is also non-contact, so there is no fouling or corrosion path. For clean water in a quiet tank with no hazardous classification, the ultrasonic EM400-UDL will usually do the same job for far less.

How long does the battery last?

The EM410-RDL is quoted at around 7 years on its 19000 mAh ER34615 cell, with a 15 minute collection interval and a 1440 minute report interval at 25 degC. The EM411-RDL uses the same cell; its datasheet does not quote a battery life figure directly, so treat the EM410-RDL number as indicative rather than specified for the ATEX model.