Endress+Hauser CM42B Liquiline Two-Wire Transmitter

CM42B Liquiline two-wire transmitter for one measuring point

The Endress+Hauser CM42B is a loop-powered, single-channel transmitter from the Liquiline range. It reads one liquid analysis sensor, either a digital Memosens sensor or, in the analog version, a conventional pH, ORP or conductivity sensor, and sends the value as a 4 to 20 mA signal with optional HART. Because it is two-wire, the same pair of conductors supplies the power and carries the signal, which makes the CM42B a natural replacement for a simple analyzer head on a long cable run. Seven Star LLC, an independent supplier in Muscat, supplies the CM42B with sensors and assemblies in Oman and the GCC.

The CM42B is offered as a field device in plastic or stainless steel housings and as a DIN-rail unit for cabinets with a separate display. The factory configuration is pH/ORP unless the "Device type" option in the order code names another parameter, and the measured parameter can be changed later in the device menu.

CM42B technical specifications

How the CM42B works with Memosens and analog sensors

With Memosens sensors the electronics are in the sensor head. The value is digitized there and sent inductively to the transmitter, which gives galvanic isolation, no contact corrosion and a watertight connection. Calibration data stays in the sensor, so a pre-calibrated sensor can be fitted on site without recalibrating the loop. The sensor also records operating hours, hours at extreme values and the number of steam sterilizations, which supports predictive maintenance.

The analog field version covers pH, ORP and inductive or conductive conductivity sensors, and an upgrade path to Memosens is available via accessories. The sensor type depends on the order. Both versions use the same operating concept: a display with a navigator and soft keys, and optional Bluetooth LE to a phone or tablet through the SmartBlue app. The Bluetooth connection is password protected, the device is not visible without the app, only a point-to-point link is made at one time, and the interface can be switched off. If it was ordered disabled, it can be released later by an activation code tied to the serial number.

Where the CM42B fits compared with other Liquiline transmitters

Pick the CM42B when one parameter is measured at one point and the plant wants a 4 to 20 mA loop. Use a CM442R or the field CM442 when two Memosens sensors, relays or a fieldbus are needed, and a CM444 or CM448 for four or eight channels. Compared with those four-wire units, the CM42B needs no mains connection at the point of measurement, which can save cable and certification effort in areas where only instrument loops are available.

A complete measuring point also needs the sensor, an assembly suited to the sensor and a measuring cable. Typical partners are CPS-type pH sensors, conductivity sensors and oxygen sensors from the same Memosens family, plus retractable or fixed holders such as the CPA875 and CPA842. The CM42B loop typically ends at a PLC or DCS analog input.

Selection checklist for a CM42B

• Housing: plastic field unit, stainless steel field unit or DIN-rail unit with a remote display.
• Sensor technology: Memosens digital or analog sensor, and the measured parameter (pH, ORP, conductivity, oxygen).
• Outputs: one or two 4 to 20 mA outputs, with or without HART.
• Bluetooth: enabled from the start or activated later.
• Hazardous area: if the installation is classified, request an Ex version and obtain its safety instructions; do not assume the standard unit is suitable.
• Cable glands: metric M20 or NPT1/2 with adapters.
• Loop supply: a supply or isolating barrier that can drive the loop within the load curve; the supply must be extra-low voltage (max. 30 V DC) with double or reinforced insulation.

Installing and commissioning the CM42B

Mount the field unit on a wall, post or pipe using the supplied mounting plate and leave clearance for the cable glands and door. Use the grounding or potential-equalization lug. The DIN-rail version belongs in a cabinet and can use the external display on a panel, connected with the 3 m RJ50 display cable, which is also the maximum permitted length.

After wiring, set the measured parameter, the engineering range for the 4 to 20 mA output, the NAMUR alarm current and damping. If HART is fitted, register the device in the asset system. Check the loop with a calibrator at 4 and 20 mA, then calibrate the sensor and note the date. The status LEDs in the housing work only when no display is connected.

Maintenance and spares for the CM42B

Routine care is limited to sensor calibration and keeping door seals clean, since the EPDM housing seals decide the IP rating. Keep spare cable glands and sealing plugs. For Memosens points, keep a pre-calibrated spare sensor and a spare Memosens cable. Record the loop output at known values so that a drift in the electronics can be spotted early against the stated tolerance.

CM42B applications in Oman and the GCC

A loop-powered transmitter is useful at remote tanks, dosing skids, boiler and cooling water sample panels, and neutralization pits where only a signal pair arrives from the control room. In Oman and the GCC the CM42B is considered for chemical dosing control, pH and conductivity monitoring in power station water loops, wastewater and effluent lines, and food and beverage hygiene steps. The stainless steel housing suits coastal air and sun exposure. For classified areas in oil and gas or petrochemical plants, an Ex version with its own documentation is required.

CM42B versions at a glance

Information to send with a CM42B request

• Measured parameter and sensor model, with Memosens or analog type
• Housing type and hazardous area classification
• Number of analog outputs and whether HART is needed
• Bluetooth enabled or disabled
• Cable gland thread and cable length
• Loop power source or barrier
• Quantity and delivery location in Oman or the GCC

Documents and quotation

The manufacturer technical information for the CM42B is attached on this page and lists outputs, tolerances, housings and the operating concept used above.

Send the order code or the application details for your CM42B and Seven Star LLC will check availability and prepare a quotation.