Engineering Guide · Vendor-Neutral

Hamilton Arc vs Mettler ISM: Which Digital Sensor Platform for Your Bioreactor?

Published September 1, 2026 · 13 min read · Specs re-verified October 4, 2026
Hamilton Arc probe-integrated transmitter versus Mettler ISM sensor + M400/M800 architecture Arc head integrated Tx Modbus RTU / 4-20 mA DCS / PLC BT Arc Wi Hamilton Arc Transmitter inside the probe head No cabinet Tx · direct Modbus to DCS VS ISM chip digital ISM digital M400 / M800 transmitter HART / PA / 4-20 mA DCS / PLC ISM Core (PC) Mettler Toledo ISM Sensor + M400/M800 transmitter Cabinet Tx · HART / PA / mA out
Figure 1: Hamilton Arc puts the transmitter inside the probe head and delivers 4-20 mA and Modbus RTU directly to the DCS, with an optional Arc Wi Bluetooth adapter for ArcAir. Mettler ISM usually keeps an M400 or M800 transmitter in the loop; the probe sends digital data over its cable, and the transmitter provides 4-20 mA, HART or a fieldbus to the plant. Same idea (intelligence in the probe), different architecture.
Quick Verdict

Choose Hamilton Arc when your automation stack is Modbus-based and cabinet space matters. The integrated transmitter head sends 4-20 mA and Modbus RTU straight to the DCS, and ArcAir on a phone, tablet or PC can calibrate and check sensors. Choose Mettler ISM when the plant is standardised on 4-20 mA/HART or fieldbus and wants named predictive diagnostics. The M400 or M800 transmitter is a familiar mediation layer, and ISM reports days to replacement, calibration and maintenance (DLI, ACT, TTM). Same underlying idea (calibration data and diagnostics live in the probe head), different architecture.

Key differences at a glance

Side-by-side comparison

Factor Hamilton Arc Mettler ISM
Where the transmitter lives Inside the probe head Separate M400 (1 channel) or M800 (1, 2 or 4 channels)
Where the intelligence lives In the probe head (calibration, diagnostics, operating hours, serial number) In the probe head (calibration, DLI, ACT, TTM, SIP/CIP counts)
Native digital output from probe Modbus RTU (RS-485) on every Arc sensor ISM digital signal to the transmitter; the InPro 6860i optical DO sensor also offers Modbus RTU
Plant-facing protocols 4-20 mA and Modbus RTU from the probe; PROFIBUS DP, PROFINET, FOUNDATION Fieldbus and OPC UA through Hamilton Arc Modbus converters; no HART route listed for Arc M400 2-wire: 4-20 mA with HART, FOUNDATION fieldbus or PROFIBUS PA. M800: eight 4-20 mA outputs plus PROFIBUS DP, PROFINET or EtherNet/IP by model
Wireless / mobile calibration ArcAir app (Windows, iOS, Android) via Arc Wi 1G or Wi 2G Bluetooth adapter fitted between sensor head and cable ISM Core PC software (successor to iSense) via iLink cable; iSense Mobile and the Bluetooth iLink are listed by Mettler Toledo as phased out
Predictive maintenance Sensor health indicators, operating hours and sterilisation counters in ArcAir Dynamic Lifetime Indicator (DLI), Adaptive Calibration Timer (ACT) and Time to Maintenance (TTM), each in days
Parameters covered under one platform DO (optical and polarographic), pH, ORP, conductivity, viable cell density (capacitance), total cell density (NIR), dissolved CO2 (NDIR) DO, pH/ORP, dissolved CO2, conductivity, turbidity, dissolved ozone, TOC (M800 parameter list)
Single-use options VisiFerm DO SU Arc; Arc Modules for single-use pH (OneFerm), conductivity and viable cell density InSUS 607 optical DO; InSUS 310i digital pH
Hardware per loop Probe and cable only for 4-20 mA or Modbus Probe, cable and a transmitter channel
Cabinet footprint per loop None for 4-20 mA or Modbus; a DIN-rail converter per up to four sensors for PROFIBUS DP or PROFINET Panel-mounted M400, or a share of a ½ DIN M800

Sources, checked October 4, 2026: VisiFerm DO Arc specification sheet, the Hamilton Arc operating instructions, Hamilton’s Arc Modbus converter range and single-use Arc Modules; Mettler Toledo’s M400 2-wire FF/PA technical data, M800 technical data, ISM Core quick setup guide and InSUS 607 page. Neither vendor publishes list prices, so this page does not quote any. Your vendor’s current datasheet takes precedence.

Hamilton Arc explained

Hamilton Arc is Hamilton Company's digital-sensor architecture in which every probe carries its own transmitter electronics inside the sensor head, which Hamilton calls the Arc MicroTransmitter. The probe converts the raw signal (luminescence quenching for optical DO, membrane potential for glass pH, RF capacitance for viable cells, non-dispersive infrared absorption for CO2) to an engineering value on board, and exposes a programmable 4-20 mA output on the cable plus a Modbus RTU (RS-485) digital channel. That is the architectural headline: no separate transmitter box. The Arc probe wires straight into a Modbus-capable input or a 4-20 mA loop, and the DCS reads engineering units directly.

How it works

The Arc family covers the common bioreactor parameters under one interface. VisiFerm DO Arc and OxyFerm FDA Arc handle dissolved oxygen (optical and polarographic respectively); EasyFerm Bio Arc covers pH; Dencytee Arc (optical density at 860 nm) and Incyte Arc (RF capacitance) split the biomass measurement between total and viable cell density; CO2NTROL measures dissolved CO2 by solid-state non-dispersive infrared absorption; Conducell Arc sensors handle conductivity. Most Arc probes share a 12 mm shaft with a PG13.5 thread and the same VP8 (or M12) cable, so a facility can standardise on one connector, one cable spec, and one Modbus interface across the parameter set.

Calibration and configuration run through software plus an optional adapter. ArcAir is Hamilton's application for Windows PCs, iOS and Android. It connects to a sensor by USB cable, or wirelessly over Bluetooth 4.0 through an Arc Wi adapter fitted between the sensor head and its cable. The Wi 1G adapter mates with a VP cable; the Wi 2G adapter uses an M12 8-pole connector to the control system and adds galvanic isolation of the two 4-20 mA outputs. Because the sensor stores its own calibration, Hamilton promotes calibrating in the lab and installing pre-calibrated sensors. ArcAir Advanced adds user management, an audit trail and electronic signatures aimed at 21 CFR Part 11. Hamilton’s manual states that values sent over the wireless link are for monitoring and maintenance, not process control.

When Arc wins

Arc fits best in three settings. Facilities designed around Modbus RTU, or PROFINET and PROFIBUS DP reached through Hamilton’s converters. The probe-direct-to-controller architecture removes the transmitter layer from the automation cabinet. Single-use bioprocessing, where the VisiFerm DO SU Arc reads a sensor element pre-installed in the bag and speaks the same Modbus RTU interface as the reusable variant, so a mixed reusable and single-use facility can run one control-system template. Multi-parameter probes on a common cable spec. A facility running viable cell density, DO, pH and CO2 on Arc across every vessel has one connector, one spares list, and one calibration app; the same four parameters on ISM need an M800 4-channel per vessel, and ISM has no capacitance probe.

Mettler Toledo ISM explained

Intelligent Sensor Management (ISM) is Mettler Toledo Process Analytics' digital-sensor platform. Where Hamilton put the transmitter inside the probe head, Mettler Toledo put the measurement and diagnostic algorithms and the digital electronics inside the probe head and kept the conversion to plant protocols in an external transmitter: the M400 for single-channel loops and the M800 in 1-, 2- and 4-channel versions that accept any compatible mix of sensors. The ISM probe sends a digital signal over the sensor cable, carrying the measured value, calibration data, sensor identity, cumulative CIP/SIP counts, and the DLI, ACT and TTM predictive-maintenance indicators.

How it works

The M400 or M800 receives the digital ISM data and converts it to a plant-facing signal. The M400 2-wire family offers 4-20 mA with HART, FOUNDATION fieldbus or PROFIBUS PA. The M800 has eight 4-20 mA outputs, a USB port, and models with PROFIBUS DP, PROFINET or EtherNet/IP. Because the transmitter mediates the protocol, an ISM probe can look identical to a legacy analog probe from the DCS’s perspective (same 4-20 mA loop) while still carrying its calibration and diagnostic data internally. That matters for retrofits into cGMP facilities that already have validated 4-20 mA I/O and want to avoid automation-side change control.

The ISM sensor library covers the standard parameters: InPro 6860i for optical DO, InPro 3253i for glass pH and ORP, InPro 5000i for dissolved CO2 (Severinghaus principle), and InPro 7100i (4-electrode) for conductivity. The InPro 6860i is unusual in that it is also sold with a direct nA or 4-20 mA/HART output and a Modbus RTU interface, so it can feed an existing biocontroller without an ISM transmitter. Calibration and asset management run through ISM Core, the PC software that replaced iSense in 2023. It connects to the sensor through an iLink cable, so sensors can be calibrated in the workshop, and it documents every calibration and maintenance step; an ISM Core CFR version targets 21 CFR Part 11. For fleets standardised on Mettler ISM, calibration records and lifetime forecasts live in one place.

When ISM wins

ISM fits best where the plant’s automation stack is already built on 4-20 mA/HART or fieldbus. Brownfield pharmaceutical retrofits where the DCS I/O, cabling, and validation package are built around 4-20 mA with HART: an ISM loop drops into that stack without automation-side change, while an Arc probe gives 4-20 mA but no HART. PROFIBUS PA loops, common on Siemens PCS 7 sites: the M400 PA connects directly, whereas Hamilton lists converters for PROFIBUS DP and PROFINET but not PA. Fleets managed as a lifecycle asset: DLI, ACT and TTM plus ISM Core’s documentation make a strong story for QA and reliability engineering, especially in facilities running dozens of loops across several product lines.

Pros and cons

Hamilton Arc

Advantages

  • Transmitter integrated into the probe head, so no cabinet transmitter and less panel space and wiring per loop
  • 4-20 mA and Modbus RTU on RS-485 directly from the probe
  • ArcAir runs on PC, iOS and Android; with an Arc Wi adapter it works over Bluetooth without a laptop
  • Broad parameter coverage on one cable spec: DO, pH, ORP, conductivity, viable and total cell density, dissolved CO2
  • Same Modbus interface on reusable and single-use variants (VisiFerm DO SU Arc, Arc Modules), so mixed fleets stay consistent

Disadvantages

  • No HART or PROFIBUS PA route listed for Arc; PROFIBUS DP, PROFINET, FOUNDATION Fieldbus and OPC UA need a Hamilton converter
  • Head electronics inside the probe raise the per-probe repair cost if the head takes a hit
  • No published day-based predictions equivalent to DLI, ACT and TTM; ArcAir reports health, operating hours and sterilisation counts
  • Bluetooth workflow needs an IT policy for mobile devices in the cleanroom or GxP area

Mettler ISM

Advantages

  • HART, FOUNDATION fieldbus and PROFIBUS PA from the M400 2-wire, and PROFIBUS DP, PROFINET or EtherNet/IP from the M800, with no extra converter
  • ISM Core PC software (successor to iSense) documents calibration and maintenance, with a CFR version for 21 CFR Part 11
  • DLI, ACT and TTM predict days to replacement, calibration and maintenance
  • Drops into existing 4-20 mA/HART I/O without automation-side change, so it suits retrofits
  • M400 and 1-channel M800 accept analog sensors too, so a fleet can migrate loop by loop

Disadvantages

  • Transmitter channel per loop, so panel space and cabling add up at scale
  • Current calibration software (ISM Core) is PC-based; the mobile iSense app and Bluetooth iLink are listed as phased out
  • No capacitance (viable cell density) probe under ISM, so biomass usually means a second vendor
  • Each loop needs a probe plus transmitter hardware, so the hardware count is higher than for an equivalent Arc loop

Which should you choose?

Four scenarios cover almost every real bioprocess sensor-platform decision. Cabinet architecture and the DCS's protocol stack drive most of the answer.

Greenfield mAb / single-use suite, Modbus- or PROFINET-native DCS

New build, several vessels, Modbus inputs or Hamilton converters to PROFINET, mix of stainless and single-use. Arc’s probe-direct-to-controller architecture removes cabinet transmitters across the whole suite.

Choose Hamilton Arc

Brownfield retrofit into 4-20 mA / HART / PROFIBUS PA plant

Existing pharmaceutical plant, validated 4-20 mA/HART loops or PCS 7 with PROFIBUS PA, no appetite for automation-side change. ISM drops in with an M400 and avoids changes to the control system I/O.

Choose Mettler ISM

Biomass capacitance + DO + pH on one platform

CHO fed-batch feed control by viable cell density, standard DO and pH loops, one connector spec across the vessel. Of these two platforms only Arc covers all three, because Mettler Toledo has no ISM capacitance probe.

Choose Hamilton Arc

QA-driven fleet asset management across 30+ loops

Multi-product commercial facility, dozens of loops, Mettler Toledo software (iSense or ISM Core) already in the QMS. DLI, ACT and TTM with ISM Core records are the operational advantage over an equivalent Arc and ArcAir fleet.

Choose Mettler ISM

Real-world use cases

Four representative setups and why the team standardised on one platform.

CHO mAb fed-batch · 2,000 L SS · Modbus
Hamilton Arc across the vessel

Example setup: VisiFerm DO Arc 225, EasyFerm Bio Arc 225 pH, Incyte Arc and CO2NTROL on PG13.5 ports. All four probes wired straight into a Modbus RTU input on the DCS. ArcAir on a tablet with Arc Wi adapters for checks at the vessel. No transmitter boxes in the automation cabinet for the sensor loops.

Legacy PCS7 API plant · PROFIBUS PA
Mettler ISM + M400 / M800

Example setup: InPro 6860i (optical DO), InPro 3253i (pH), InPro 5000i (CO2) on ISM cables into M400 PA transmitters on the existing PROFIBUS PA segment. ISM Core CFR on a QA-controlled PC holds the calibration records. The retrofit drops straight into the existing PA fieldbus.

Single-use CHO clinical suite · 200 L SU
Mostly Arc, with a mixed-vendor DO story

Example setup: a 200 L single-use stirred tank whose bag carries either the bag vendor’s own pre-installed optical DO sensor or a Hamilton VisiFerm DO SU Arc sensor element, depending on the bag configuration. Arc Modules for single-use pH and viable cell density keep one Modbus interface. See our Hamilton VisiFerm vs PreSens comparison for the probe vs spot decision inside the single-use bag.

Bench PD lab · 8 × 2 L glass · flexibility
Whichever platform the lab already runs

At bench scale the differentiators shrink. A PD lab usually inherits the sensor line its bioreactor controller supports and does not switch. If the lab has both, a common split is Arc for viable cell density (Mettler Toledo has no capacitance probe) and whichever platform the controller already reads for DO and pH.

Not sure which sensor set fits your scale, modality, and automation stack?

Answer a few questions about vessel, parameters, protocol, and budget and get a ranked sensor recommendation across both digital platforms, plus single-use and non-invasive alternatives.

Open the Sensor Selection Tool

Cost and lifecycle considerations

The cost comparison depends on how many transmitters you can avoid

Neither vendor publishes list prices, so we do not quote any; ask both for a quote on the same loop count. The structural difference is the transmitter and the cabinet space. A 12-loop suite on Arc needs no separate transmitters for 4-20 mA or Modbus; the same suite on ISM needs 12 M400s, or three 4-channel M800s, plus the panel space and wiring to house them. On the other hand, an ISM retrofit into an existing 4-20 mA/HART plant reuses the existing I/O and cabling, while an Arc retrofit gives 4-20 mA without HART, or needs Modbus-capable inputs or a Hamilton converter.

Calibration labour is broadly similar, because both platforms store the calibration on the probe head and both allow calibration in the workshop before installation. Arc gains on transmitter avoidance; ISM gains when reusing an existing 4-20 mA/HART or PROFIBUS PA infrastructure outweighs that.

Two smaller lifecycle items are worth mentioning. Because the transmitter is inside the Arc probe head, a physical impact to the head can mean replacing the whole probe rather than just a transmitter, so mechanical protection of the head matters more in operator-heavy areas. Conversely, an ISM installation has one more component in the loop (the transmitter) that can fail or need configuring.

Cost component (per loop) Hamilton Arc Mettler ISM
Probe (DO example: VisiFerm DO Arc 225 vs InPro 6860i)Quote requiredQuote required
TransmitterNone (integrated)M400, or one channel of an M800
Cabinet space per loopNone for 4-20 mA or Modbus; shared DIN-rail converter for PROFIBUS DP or PROFINETPanel-mounted M400 or a share of a ½ DIN M800
CalibrationArcAir on PC or mobile, in the lab or at the vesselISM Core on PC via iLink, in the workshop; or at the transmitter
Fieldbus without extra hardwareModbus RTU onlyHART, FOUNDATION fieldbus, PROFIBUS PA (M400); PROFIBUS DP, PROFINET, EtherNet/IP (M800)

Sources: the hardware and protocol rows follow the vendor documents listed under the side-by-side table. Prices are not published by either vendor and are therefore not shown.

Product families and adjacent platforms

Both vendors ship broad product lines under their digital-sensor banners. Below is the one-line positioning for each, plus the adjacent digital platforms worth knowing about.

Hamilton Arc family

Mettler Toledo ISM family

Adjacent digital platforms

Frequently asked questions

What is the difference between Hamilton Arc and Mettler ISM?
Both are digital sensor platforms that store calibration data, diagnostics and the serial number in the sensor head rather than in the transmitter. The difference is where the signal is turned into a plant-facing output. Hamilton Arc builds the transmitter into the sensor head, so the probe itself delivers a 4-20 mA signal and Modbus RTU over RS-485 and needs no separate transmitter box. Mettler Toledo ISM sensors normally send their digital ISM signal over the sensor cable to an ISM transmitter such as the M400 or M800. The M400 2-wire family then outputs 4-20 mA with HART, FOUNDATION fieldbus or PROFIBUS PA, and the M800 outputs 4-20 mA plus PROFIBUS DP, PROFINET or EtherNet/IP, depending on the model. Some ISM sensors bridge the gap: the InPro 6860i optical DO sensor is also sold with a direct nA or 4-20 mA/HART output and a Modbus RTU interface. Arc reduces cabinet hardware; ISM keeps the transmitter as a familiar layer for 4-20 mA and fieldbus plants.
Does Hamilton Arc need a transmitter?
No. Every Arc sensor (for example VisiFerm DO Arc, OxyFerm FDA Arc, EasyFerm Bio Arc pH, Incyte Arc, Dencytee Arc, Conducell Arc conductivity and CO2NTROL) has the transmitter electronics in the sensor head. The VisiFerm DO Arc datasheet lists a programmable 4-20 mA output and an RS-485 Modbus interface on the sensor cable. For other networks Hamilton sells Arc Modbus converters for PROFIBUS DP, PROFINET, FOUNDATION Fieldbus and OPC UA. Hamilton does not list a HART converter for Arc; its HART option for dissolved oxygen is the separate 2-wire VisiFerm mA sensor for hazardous areas. An Arc probe can therefore be wired straight into a 4-20 mA or Modbus-capable input with no transmitter box.
What transmitter does Mettler ISM use?
ISM sensors connect to an ISM-capable transmitter or bioreactor controller. In bioprocess plants the usual choices are the single-channel M400 and the M800, which comes in 1-, 2- and 4-channel versions. The ISM sensor sends its measured value, calibration data and diagnostics digitally over the sensor cable. The M400 2-wire family outputs 4-20 mA with HART, FOUNDATION fieldbus or PROFIBUS PA; the M800 has eight 4-20 mA outputs and models with PROFIBUS DP, PROFINET or EtherNet/IP. The M400 and the 1-channel M800 also accept analog sensors (mixed mode), so a fleet can be migrated loop by loop. Some ISM sensors, such as the InPro 6860i optical DO sensor, are also available with a direct analog output for existing biocontrollers and analog transmitters.
Can I mix Hamilton Arc and Mettler ISM sensors in one facility?
Yes. Both platforms can deliver a 4-20 mA signal to the control system, so Arc probes and ISM loops can sit in the same DCS without special integration work. The cost of a mixed fleet is in maintenance: your team needs to be trained on ArcAir (Hamilton's PC and mobile software) and ISM Core (Mettler Toledo's PC software, the successor to iSense) and to stock spares for both. For that reason it is common to standardise on one platform per parameter, for example Arc DO probes everywhere and ISM pH everywhere, rather than one platform per vessel.
Is ArcAir the same as iSense?
No. ArcAir is Hamilton's software for configuring, calibrating and monitoring Arc sensors. It runs on Windows PCs and on iOS and Android devices, and connects by USB cable or by Bluetooth through an Arc Wi adapter that fits between the sensor head and its cable. iSense was Mettler Toledo's PC software for ISM sensors. In 2023 Mettler Toledo replaced it with ISM Core, which connects to the sensor through an iLink cable so it can be calibrated away from the process, and shows the Dynamic Lifetime Indicator (DLI), Adaptive Calibration Timer (ACT) and Time to Maintenance (TTM). Mettler Toledo's mobile route, iSense Mobile with Bluetooth adapters, is now listed among its phased-out products. Both tools keep an audit trail, and both vendors offer versions aimed at 21 CFR Part 11 work (ArcAir Advanced and ISM Core CFR).
Which platform is more common in cGMP commercial manufacturing?
Both are used in cGMP manufacturing. Neither vendor, nor any independent source we could find, publishes installed-base figures, so we do not rank them. The practical answer depends on what is already on site. A plant built around Mettler InPro sensors and 4-20 mA/HART or PROFIBUS PA loops can add ISM sensors without changing its automation layer, while a Modbus-based skid or a new build that wants fewer transmitter boxes fits Arc more naturally. For new builds the choice usually comes down to whether the facility standardises on classical 4-20 mA/HART and fieldbus (advantage ISM) or on Modbus and Ethernet-based networks reached through converters (advantage Arc).
Does either platform support single-use bioreactors?
Yes, both vendors have single-use options, built differently. Hamilton's VisiFerm DO SU Arc is a reusable optical reader that sits outside a gamma-sterilised sensor element pre-installed in the bag and never touches the medium. Hamilton also offers Arc Modules for single-use pH (OneFerm), conductivity and viable cell density (Incyte). All provide Modbus RTU, and the DO, pH and conductivity versions also provide a 4-20 mA signal. Mettler Toledo's single-use line is InSUS: the InSUS 607 optical DO sensor mounts on a standard 1-inch Eldon James port disc for bags of 20 to 3,000 L, and the InSUS 310i is a digital single-use pH sensor. We found no single-use dissolved CO2 sensor from either vendor. For non-invasive sensor spots read through the bag wall, see our Hamilton VisiFerm vs PreSens comparison.
Which platform has better predictive-maintenance analytics?
Mettler Toledo has the more developed set of named indicators. ISM sensors report the Dynamic Lifetime Indicator (DLI, days until the sensor or a replaceable part should be exchanged), the Adaptive Calibration Timer (ACT, days until the next calibration) and Time to Maintenance (TTM, days until cleaning or maintenance), and Mettler Toledo publishes a white paper on how DLI and ACT are calculated. Hamilton Arc sensors also store calibration and diagnostic data in the head, and ArcAir shows sensor health indicators, operating hours and sterilisation counters, but Hamilton does not publish an equivalent set of day-based predictions. For a fleet at commercial scale, the deciding factor is usually which software your QA and maintenance systems already use.

Resources and references

Further reading