Precision Digital PD685 Intrinsically Safe IP67 Loop-Powered Meter

The Precision Digital PD685  is an ATEX and IECEx intrinsically safe, IP67 loop-powered digital indicator that is easy to install and program. It can be seen from a considerable distance in bright sun or dimly lit areas when the standard backlight feature is activated. The fact that this meter is loop-powered means that there is no need to run additional, costly power lines into a hazardous area. The meter gets all of the power it needs from the 4-20 mA loop and its 1 V (4 V with backlight) drop results in a minimal burden on the loop. The meter features a wide -40°C to +75°C operating temperature range and is available with a 22 mm (0.865″) conduit hole in a location of your choice for easy installation. Calibration is a quick two-step process involving the adjustment of only two sets of coarse and fine, non-interacting potentiometers.


  • NEMA 4, IP67 Loop-Powered Field-Mount Process Meter
  • 4-20 mA Input
  • 1.1″ (28 mm) 3½ Digits LCD Display; -1999 to 1999
  • 1 V Drop (4 V Drop with Backlight)
  • HART® Protocol Transparent
  • Loop-Powered Backlight Standard
  • Operates from -40 to 75°C (-40 to 167°F)
  • Coarse and Fine Zero & Span Potentiometer Adjustments for Easy Field Scaling
  • Plastic NEMA 4, IP67 Enclosure
  • ATEX and IECEx Certified as Intrinsically Safe
  • CE Marked
  • Conformal Coated PCBs for Dust and Humidity Protection
  • One ½” Conduit Hole (Rear, Top, Bottom or None)
  • Pipe & Panel Mounting Kits
  • Stainless Steel Tag Available

Conduit Installation Instructions

  1. Remove the printed circuit board from the enclosure.
  2. Connect appropriate size conduit fittings to the hole provided. For enclosures without a pre-drilled hole, the installer must make a hole in accordance with the instructions for the particular conduit fitting being installed.
  3. Connect conduit (with attached hubs) to the enclosure. Conduit hubs must be connected to the conduit prior to being connected to the enclosure. Use only conduit hubs that are designed to maintain NEMA 4 or IP67 ratings.

Note: Please read PD685 Intrinsic Safety Control Drawing (LIM685-2) for more information pertaining to the conduit holes.

Mounting Instructions

  1. Remove the enclosure cover from the base.
  2. Insert mounting hardware into mounting holes in enclosure base.
  3. Secure the enclosure base to the mounting surface using the inserted hardware.
  4. Re-attach the enclosure cover to the base.


The only tools needed for calibration are a calibrated current source and a small slotted/flathead screwdriver.

Calibration Connections

To access the input terminals it is necessary to remove the enclosure cover and the printed circuit board. This is done by loosening the four screws on the enclosure cover and removing the cover. Completely loosen both thumb screws that hold the printed circuit board to the enclosure. Turn it over to gain access to the reverse side. Then, proceed to connect a calibrated current source.

Decimal Point Selection

The decimal point jumper array J2 is located in the lower right corner of the printed circuit board next to the display. It is labeled DDD.D, DD.DD, and D.DDD. Place a jumper over both pins of DDD.D for a display of 199.9, DD.DD for 19.99, or D.DDD for 1.999.


LO and HI coarse and fine calibration controls are located below the display. The meter is factory calibrated to display -500 at 4 mA and 1500 at 20 mA. Use the HI and LO COARSE controls for large range changes during calibration and the HI and LO FINE controls for precision changes. Apply a 4 mA signal and adjust the LO controls to display the desired reading. Apply a signal between 16 and 20 mA and adjust the HI controls to display the desired reading. Complete the calibration procedure by making minor adjustments to the LO and HI controls as necessary.


Installation of the meter involves removing the printed circuit board from its enclosure and connecting a ½” conduit fitting to the hole provided. Refer to PD685 ATEX and IECEx Certified Loop-Powered Meter Intrinsic Safety Control Drawing diagrams (LIM685-2) for further details. Wall mounting holes are located in each corner of the enclosure.

Loop Connections

Disconnect power to the loop and wire the meter as illustrated in Figures 3 & 4 for 2-wire transmitter configuration, Figures 5 & 6 for 4-wire transmitter configurations, and the PD685 ATEX and IECEx Certified Loop-Powered Meter Intrinsic Safety Control Drawing diagrams (LIM685-2) supplied with the instrument. Connect the loop return wire to S- to disable the backlight feature or connect it to B- to enable the backlight feature.


Except where noted all specifications apply to operation at +25°C.
Input: 4-20 mA @ 30 VDC maximum
Display: 28 mm (1.1″) LCD, 3½ digits; -1999 to +1999
Backlight: Powered by 4-20 mA loop. Intensity varies with signal level
Accuracy: ±0.1% FS ±1 count
Entity Parameters: Ui = 30 V, Ii = 175 mA, Pi = 1 W, Ci = 0, Li = 0
Decimal Point: User selectable via J2 jumper
Calibration: Four-step coarse and fine control; non-interacting zero and span
Calibration Range: 4 mA input: -1000 to +1000; 20 mA input: between 20 and 2000 counts > 4 mA display
Display Update Rate: 2.5/second
Maximum Input Current: 30 mA
Input Overload Protection: Over voltage protection to 30 V max (between S+ and S-)
Maximum Voltage Drop: 1 V @ 20 mA (4 V @ 20 mA with backlight)
Operating Temperature: -40°C to +75°C
Storage Temperature: -40°C to +85°C
Relative Humidity: 0 to 90% non-condensing. Printed circuit boards are conformally coated.
Enclosure: Impact-resistant, glass-filled, polycarbonate body, opaque; Impact-resistant, polycarbonate cover, transparent; Polyurethane/polymer gasket; Polyamide/plastic cover screws; NEMA 4X, IP67
Connections: Removable screw terminal block, 12 to 24 AWG.
Conduit Hole: One 22 mm (0.865″) conduit hole may be provided; refer to Ordering Information to specify conduit size and hole location; request sku (-Z) for no conduit hole.
Weight: 340 g (12 oz)
Warranty: 2 years parts & labor

Compliance Information

Product Markings:

 II 1 GD
Ex ia IIC T4 Ga
Ex ia IIIC T135°C Da
-40°C ≤ Ta ≤ +75°C; IP67

Special Conditions for Safe Use:

  1. The permitted ambient temperature range for the PD685 is -40°C to +75°C (-40°F to 167°F).
  2. Use suitably certified and dimensioned cable entry device and/or plug. The equipment shall be installed such that the supply cable is protected from mechanical damage. The cable shall not be subjected to tension or torque.
  3. Under certain extreme circumstances, the non-metallic parts incorporated in the enclosure of this equipment may generate an ignition-capable level of electrostatic charge. Therefore, the equipment shall not be installed in a location where the external conditions are conducive to the build-up of electrostatic charge on such surfaces. This is particularly important if the equipment is installed in a zone 0 location. In addition, the equipment shall only be cleaned with a damp cloth.
  4. The cable entry into the enclosure shall be by means of conduit or cable gland and shall provide a minimum degree of protection of IP5X.

Year of Construction: This information is contained within the serial number with the first four digits representing the year and month in the YYMM format.
For European Community: The PD685 must be installed in accordance with the Essential Health & Safety Requirements of Directive 2014/34/EU, the product certificates CML 17ATEX2113X and IECEx CML 17.0052X, and the product manual. All controls and wiring connectors are accessed by opening the enclosure. To access electrical connectors, remove the enclosure cover, unscrew the two captive screws that fasten the printed circuit board, and remove the printed circuit board from the enclosure.


Figure 1: Calibrator Connection
Figure 2: Calibration Controls Location

Two-Wire Transmitter Input

Figure 3: Control Loop Connections (2-Wire)
Figure 4: Control Loop Connections with Backlight (2-Wire)

Four-Wire Transmitter Input

Figure 5: Control Loop Connections (4-Wire)
Figure 6: Control Loop Connections with Backlight (4-Wire)

Dimensions and Wall Mounting

A: 80 mm (3.15″)C: 62 mm (2.44″)E: 70 mm (2.75″)
B: 130 mm (5.12″)D: 112 mm (4.41″)F: 20 mm (0.79″)

Pipe Mounting Kit

The PDA6845 is a pipe mounting kit with two mounting holes. It provides all of the necessary hardware to mount the PD685 to a 2″ pipe. It is available in zinc plated and stainless steel materials.

Panel Mounting Kit

The PDA6854 is a panel mounting kit for the PD685. It provides all of the necessary hardware to mount the PD685 meter to an equipment panel. This panel mounting kit is not intended to provide waterproof protection to the panel.

Instruction Manual:LIM685_1 Instruction Manuals


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