Honeywell XNX Universal Transmitter Wiring Diagram Guide and Installation Steps
Start by locating the terminal block on the rear panel–it’s marked with 8 labeled ports arranged in two columns. Left side: +U, -U, Ai1+, Ai1-, Ai2+, Ai2-. Right side: F+, F-, C. Connect the power source to +U (24V DC) and -U (ground) first–reverse polarity risks permanent damage to the internal circuitry.
For 4-20mA analog output, wire the primary sensor to Ai1+ (current source) and Ai1- (return). Ensure the loop resistance stays below 600 ohms–exceeding this threshold distorts readings. Secondary channels (Ai2) accept voltage input (0-1V or 0-5V) if jumper JP4 is set to V–check the configuration sticker on the device lid before proceeding.
The fault relay outputs follow a dry-contact design: C (common), F+ (normally open), F- (normally closed). Use 18-22 AWG copper wire for connections–thinner gauges introduce voltage drops, causing false alarm triggers. Test the relay operation with a multimeter in continuity mode before integrating into safety circuits.
Communication protocols require separate grounding: RS-485 uses terminals 1-4 (A+, B-, GND, shield), while HART loops through the Ai1+/Ai1- pair. Terminate RS-485 lines with a 120-ohm resistor at both ends of the bus–omitting this causes signal reflections and transmission errors.
Verify all connections with a calibrated meter before powering up. Measure 4mA at Ai1+ when no gas is present–values below 3.8mA indicate a broken loop or incorrect scaling in the controller. For digital integration, consult the protocol-specific header file (Modbus RTU registers start at 40001, HART commands use universal polling addresses).
Guide to Connecting the Honeywell Gas Detection Device: Electrical Schematics
Before handling any terminals, power down the system by disconnecting the main supply at the circuit breaker. Verify absence of voltage using a multimeter set to AC measurement–readings above 10V indicate unsafe conditions. The 4-20mA output signal requires a shielded twisted pair cable with a minimum cross-sectional area of 0.5 mm². Route cables away from high-voltage lines and inductive loads; a separation of at least 30 cm prevents signal interference.
- Pin 1 (V+): Connect to the positive terminal of a 24VDC power source. Use a fuse rated for 500mA as overcurrent protection.
- Pin 2 (4-20mA+): Attach to the input channel of the PLC or data logger. Ensure the receiving device’s impedance does not exceed 500 ohms.
- Pin 3 (SGD): Ground reference. Bond to the system’s earth ground using a 1.5 mm² copper cable, terminated at the nearest grounding busbar.
- Pin 4 (4-20mA-): Return path for the current loop. Must not be connected to ground; float this terminal relative to earth.
Common Pitfalls and Corrections
Incorrect polarity reversal between pins 2 and 4 disrupts signal integrity–double-check connections with a continuity tester. If the signal drifts or fluctuates, inspect cable routing for proximity to variable frequency drives or motors; relocate or shield cables if necessary. Transient voltage suppressors rated for 30V should be installed across the power input if the supply originates from a switch-mode source.
For installations in hazardous zones, consult the specific certification drawings (ATEX/IECEx) before terminating conduits. Seal glands must comply with ingress protection standards (IP66/67). Test loop integrity under load by simulating a mid-range signal (12mA) and verifying reception at the controller within ±0.1mA tolerance. Record baseline values for future diagnostics.
Identifying Terminal Blocks on the Gas Detection Device for Sensor Integration
Locate the main connection interface on the device’s rear panel–marked by a hinged cover labeled “Sensor Terminals.” Remove the cover to expose two rows of screw-type clamps, numbered sequentially from left to right. The upper row handles signal output, while the lower row manages excitation and reference inputs. Verify the presence of a grounding lug adjacent to terminal 1, essential for noise reduction in 4-20 mA loops.
Refer to the following terminal assignments for common sensor types. Note that deviations exist for specialized probes–consult the probe-specific documentation for anomalies.
| Terminal Number | Function (Standard Sensors) | Wire Color (Default) |
|---|---|---|
| 1 | Signal (+) | Red |
| 2 | Signal (-) | Black |
| 3 | Excitation (+) | White |
| 4 | Excitation (-) | Green |
| Ground Lug | Chassis Ground | Bare/Yellow-Green |
For catalytic bead sensors, terminals 3 and 4 provide the Wheatstone bridge voltage. Ensure the excitation wires (typically 3 volts) match the sensor’s datasheet to prevent false readings or damage. For electrochemical cells, terminals 3 and 4 may remain unused, as these sensors are self-powered–adhere strictly to the polarity marked on the cell’s label.
Troubleshooting Mismatched Terminals
Check for loose connections first–oxidized or under-torqued screws account for 60% of signal integrity issues. Use a torque screwdriver at 0.5 Nm to secure wires without stripping threads. Test continuity with a multimeter between the sensor’s connector and the device’s terminals; resistance above 0.5 ohms indicates a faulty or corroded connection. Replace degraded wires rather than re-terminating them–soldered joints introduce thermal noise in low-level signals.
For multimode units, confirm jumper settings on the internal PCB before wiring. A removable label inside the terminal cover details jumper positions for voltage (V), current (I), or frequency (F) outputs. Incorrect settings void sensor calibration, though the device will not indicate an error–validate output type before powering the system.
Step-by-Step Wiring Configuration for 4-20mA Output with HART
First, identify the signal source terminals on the device: typically marked as “+” (positive) and “-” (negative) for current loop connections. For HART communication, ensure the loop resistance falls between 250Ω and 600Ω–this range guarantees reliable protocol transmission without signal degradation. If the existing load resistor exceeds 600Ω, replace it with a precision 250Ω resistor to maintain compatibility.
Connect the positive terminal of the sensor’s output to the positive input of the current loop. Use twisted-pair shielded cable (minimum 22 AWG) to minimize electromagnetic interference, especially in industrial environments with high noise levels. Ground the cable shield at one end only–preferably at the signal conditioner or control system–to prevent ground loops.
Configuring HART Communication
Wire the HART network in parallel to the 4-20mA loop: attach the HART modem’s “+” terminal to the loop’s positive line and its “-” terminal to the negative line. Avoid adding resistive or capacitive components to this path, as they can disrupt the high-frequency HART signals. Verify the device’s default HART address; most models use address 0 unless reconfigured. If multiple devices share the loop, assign unique addresses to prevent conflicts.
Power the loop with a 24VDC supply, ensuring the voltage complies with the sensor’s specifications–some models require a minimum of 12VDC drop across the device. Use a regulated power source with less than 100mV ripple to prevent erratic readings. For intrinsic safety applications, select a barrier with an entity parameter matching the sensor’s power requirements (e.g., 80mA maximum for standard configurations).
The correct polarity is critical: reverse connections will prevent both the 4-20mA signal and HART communication from functioning. Test continuity with a multimeter before powering the loop–resistance should read ~250Ω (or your chosen load resistor value) when the circuit is complete. If HART communication fails, check for loose connections or excessive loop resistance; a broken shield can also introduce noise, masking the HART signal.
Final Validation
Once wired, initiate a loop test by measuring the current at the receiver end. A functioning 4-20mA output should vary between 3.8mA (low end) and 20.5mA (high end), with HART data overlaid as a 1200Hz frequency shift. Use a HART communicator or host software to query the device–successful communication confirms proper wiring. If the current reads erratically, isolate the loop components one by one to identify the fault.
For redundant safety, add a fuse rated below the sensor’s maximum current (e.g., 25mA) in series with the positive line. This protects both the sensor and control system from overcurrent conditions. In installations requiring galvanic isolation, use an isolating device between the HART modem and the current loop to prevent ground loops–opt for models with built-in signal repeaters if the loop exceeds 1,000 feet.
Power Supply Requirements and Grounding Best Practices
Ensure a dedicated 24 VDC power source with a minimum 20 mA current capacity per connected sensor loop, accounting for signal conditioning modules if present. Stabilized supplies below 22 VDC may induce measurement drift; verify ripple does not exceed 50 mV peak-to-peak under full load conditions.
Isolate each channel using separate secondary windings on a multi-tap transformer or individual DC-DC converters meeting IEC 61000-4-4 surge immunity (4 kV, 5/50 ns). Bypass capacitors rated 0.1 μF ceramic and 10 μF electrolytic must be mounted within 2 cm of sensor terminals to suppress transient noise.
Ground reference loops through a star topology, converging at a single earth point bonded to the facility grounding system with a resistance below 0.1 Ω. Avoid daisy-chaining–each sensor channel’s return path should terminate directly at the common star point without intermediate splices.
Twisted shielded pair cable must maintain consistent 18 AWG conductor gauge; shielding coverage exceeding 90% should be bonded only at the control system end to prevent ground loop formation. For runs exceeding 30 m, employ shield drain wire connected at both ends with impedance-matched terminators.
Field devices operating in hazardous areas require intrinsically safe barriers with entity parameters exceeding 80 mA current and 0.2 W power dissipation. Verify barrier clamping voltage aligns with sensor input span (±30 mV tolerance) and avoids exceeding 30 VDC in fault conditions.
Surge protection devices for outdoor installations should conform to IEC 61643-21:2000 (Class II), capable of diverting 10 kA (8/20 μs) transients. Install arrestors at both cable entry and equipment terminals, maintaining less than 1 m lead length to prevent inductive voltage spikes.
Before energizing, measure loop resistance between signal positive and negative terminals; deviations above 10 Ω indicate faulty terminations or cable breaks. Record baseline noise floor across sensor inputs in no-load state–acceptable thresholds remain below 1 mV RMS for standard 4-20 mA loops.