Measuring Conductivity, Resistivity and Salinity with the Multi- Parameter Input Transmitter

The DPU91 transmitter provides a single channel interface for various types of parameters, including flow, conductivity/resistivity, pH/ORP, temperature, and salinity. The DPU91-BC transmitter has the additional capability to support the batch module for batching control.

The DPU91 transmitter has the extra-large (3.90 x 3.90") autosensing backlit display that can be viewed at 4 to 5 times the distance compared to conventional transmitters. The well-illuminated display and large characters lower the risk of misinterpreting or misreading the displayed values.

Separate lines for main, units, secondary measurements, and “dial-style” digital bar graph are shown in the display. The DPU91 transmitter is available in field or panel-mount versions, and both of these configurations can operate on 12 to 32 VDC power (24 VDC nominal) and provide 4 to 20 mA outputs.

Designed for full flexibility, plug-in modules enable the unit to easily adapt to varying needs of customers. Batch, relay, direct conductivity/resistivity, and a PC communications configuration tool are available as optional modules. The unit can be used together with default values for easy and fast programming or can be modified with adjustable minimum and maximum dial settings, labeling, unit and decimal measurement options.

  • Intuitive and “user-friendly” interface
  • “Dial-Style” digital bar graph
  • Large auto-sensing backlit display
  • Warning LED indicator
  • Custom 13-character label capabilities
  • Factory reset capability
  • Optional field upgradable relays



  • Input Channels: 1
  • Input Types: Digital serial ASCII, TTL level, 9600 bps
  • Frequency Range: 0.5 to 1500 Hz
  • Accuracy: 0.5% of reading (display)
  • Measurement Types: Flow, pH/ORP, conductivity/resistivity, salinity, pressure, temperature or batch
  • Enclosure and Display
  • Case Material: PBT
  • Window: Shatter-resistant glass
  • Keypad: 4 buttons, injection-molded silicone rubber seal
  • Display: Backlit, 7 and 14-segment
  • Update Rate: 1 second
  • LCD Contrast: 5 settings
  • Indicators: “Dial-style” digital bar graph, LEDs for open collector, relays and warning indicator
  • Enclosure: ¼ DIN, NEMA 4X/IP65
  • Mounting Panel: ¼ DIN, ribbed on four sides for panel mounting clip inside panel, silicon gasket (included)
  • Field Mounts: Specified to Omega® field mount junction boxes
  • Weight: 0.63 kg (1.38 lb)
  • Display Ranges:
    • For PH/ORP version visit
    • For flow version visit dpu91_flow
  • Conductivity: 0.0000 to 99999 µS, mS, PPM and PPB (TDS), kO, MO
  • Conductivity Temperature: -99 to 350 °C (-146 to 662 °F)
  • Temperature: -99 to 350 °C (-146 to 662 °F)
  • Salinity: 0 to 100 PPT


  • Ambient Operating Temperature:
    • Backlit LCD: -10 to 70 °C (14 to 158 °F)
    • Storage Temperature: -15 to 70 °C (5 to 158 °F)
  • Relative Humidity: 0 to 100% condensing for field mount; 0 to 95% non-condensing for panel mount
  • Maximum Altitude: 4000 m (13,123')

Electrical Requirements

  • Power to Sensors:
    • Voltage: 4.9 to 5.5 VDC @ 25 °C, regulated short circuit protected
    • Terminal Blocks: Pluggable screw type 14 AWG maximum wire gauge

Input Power

  • DC: 10.8 to 35.2 VDC, regulated
  • Current Output:
  • 4 to 20 mA (10.8 to 35.2 VDC, 30 mA max)
  • Open Collector: 1
  • Overvoltage Protection: 48 V transient protection device current limiting for circuit protection and reverse-voltage protection

Relay Specifications (DPU91-R)

  • Dry-Contact Relay:
  • Type: SPDT, Form C
  • Maximum Current Rating: 5 A resistive 50 mA DC
  • Maximum Voltage Rating: 30 VDC or 250 VAC
  • Hysteresis Adjustable: Absolute in engineering units (EUs)
  • Latch Reset: In test screen only
  • Delay: 9999.9 seconds (maximum)
  • Test Mode: Set on/off
  • Cycle Time: 99999 seconds (maximum)
  • Maximum Pulse Rate: 400 pulses/minute
  • Proportional Pulse: 400 pulses/minute
  • Volumetric Pulse Width: 0.1 to 3200 s
  • Pulse Width Modulation: 0.1 to 320 s

Input Types

  • Digital or AC Frequency: pH/ORP input via the digital output from the PHTX-2750 pH/ORP sensor electronics for pH/ORP models visit dpu91_ph. For flow models visit
  • Raw Conductivity/Resistivity: Input directly from signet conductivity/ resistivity electrodes via direct conductivity/resistivity module or via CDTX-2850

Input Specifications

  • Digital Serial: ACSII, TTL level, 9600 bps
  • Frequency Input:
    • Sensitivity: 80 mV @ 5 Hz, gradually increasing with frequency
    • Span: 0.5 Hz to 1500 Hz @ TTL level input
  • Accuracy: ± 0.5% or reading maximum error @ 25 °C (77 °F)
  • Resolution: 1 µS
  • Repeatability: ±0.2% of reading

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