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Honeywell DL421/422 DirectLine® Sensor

DirectLine® Sensor

The Honeywell DirectLine® architecture consists of an electronics module integral to the electrode. This design eliminates the need and added cost of a separate analyzer or transmitter.

The electronics module is sealed in a plastic weather proof, corrosion resistant housing and is connected to the pH/ORP electrode on one side and a 4-20 mA output cable on the other via water proof connectors. This housing design allows this system to be used in harsh environments where moisture and dust is a problem.

For submersion or special mounting applications, the remote mounting option connects the electronics module to the electrode via a cable. The electronics module is then mounted on a 2-inch pipe, wall, or DIN rail.

• Direct 4-20 mA output eliminates need for dedicated analyzers or transmitters, simplifying installation, start-up, operation, and maintenance tasks. Installation costs are also reduced because standard cable can be used for additional cable distances.
• Integral electronics with local HMI simplifies installation and shortens calibration times.
• Modular plug-in construction simplifies electrode replacements.
• Local display and keypad facilitates quick set-up, calibration, and operational activities.
• ½” NPT conduit connection provides increased protection and noise immunity of output cable
• Plug-in modular design allows sensor to be safely removed and replaced without cycling power on the electronics module.
• Electronics and sensor diagnostics reduces troubleshooting times.
• Sample or auto buffer calibration options accommodates individual calibration techniques and reduces calibration time.
• Playing card-sized guide facilitates simple, correct, and consistent calibration and configuration.
• Watertight sensor connection for reliability in submersion applications.
• Global approvals including:
    – CE Mark for industrial applications
    – UL General Purpose
    – CSA General Purpose
    – FM Class I, Div. 1 (I.S.)
    – FM Class I, Div. 2 (non-incendive field wiring)
    – IP66, Type 4x Enclosure

Displayed Process Variable pH: 0-14 pH
ORP: –1600 to +1600 mV
Displayed Temperature Range
(pH only)
–10 °C to +110 °C (14 °F to 230 °F)
Display Accuracy (reference) pH: ±0.02 pH
ORP: ±1 mV
Process Temperature Durafet®: –10 °C to +110 °C (14 °F to 230 °F)
Meredian®: 0 °C to 110 °C (32 °F to 230 °F)
Durafet® Sensor Survivable
Temperature Range
–10 °C to +130 °C (14 °F to 266 °F)
Electronics Module Ambient
–20 °C to +85 °C (–4 °F to +185 °F)
Output Type 4-20 mA (2-wire loop powered)
Output Scale 0-14 pH, ±1600 mV
Output Calibration 4-20 mA
Durafet® Remote Mating
Connector Rating
Submersible to 20 feet
Output (Loop) Cable
M12 type
User Termination Tinned leads on cord set or customer supplied cable
Cable Lengths Sensor: Durafet®: 20 feet or 50 feet
Meredian®: 12 feet or 20 feet
Output: 20 feet or 50 feet
Power 16-42 Vdc
Maximum Load Resistance:
250 ohms at 16 Vdc
600 ohms at 24 Vdc
1400 ohms at 42 Vdc
Local Display and Buttons LCD 4-digit, 7-segment
Engineering Units pH, mV
degrees F
degrees C
Calibration Options (pH) 1 point Sample or 2 point Sample
Auto Buffer Recognition
Selections: US, NIST, EURO
Solution Temperature
Compensation (for pH only)
Selections: 0.00pH/10 °C
–0.16pH/10 °C
–0.32pH/10 °C
Diagnostics Sensor and electronics
Case Weatherproof, corrosion-resistant plastic housing
Approvals CE Mark for Industrial Applications
UL – General Purpose
CSA – General Purpose
FM Class I, Div. 1, Groups A, B, C, D and Class I, Zone 0, AEx ia IIC (I.S.)
FM Class I, Div. 2, Groups A, B, C, D; Class I, Zone 2, Groups IIC (non-incendive field wiring)
Enclosure: IP66, Type 4x
Remote Mounting Pipe, Wall, or DIN Rail
Dimensions H 123 mm (4.84") x W 48 mm (1.89") x D 46 mm (1.81")
Weight Approximately 142 g (5.0 oz.)

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