Delavan Cap Analog 421 Level Transmitter

Delavan Cap Analog 421  Level Transmitter

Delavan’s Cap Analog 421 series is a Continuous Level Transmitter for liquids, slurries, and powder bulk solids. The 421 has the ability to display and transmit a continuous level measurement with optional hi or low-level alarms on one sensing element.

Delavan’s Capacitance Cap Analog 421 system uses a compact pre-amplifier mounted on the rear of the probe assembly. The pre-amp is housed in a cast aluminum enclosure that is weather-tight and explosion-proof. All other electronic hardware is located in the remote NEMA 4X housing. All calibration adjustments are made at the remote location.

The Cap Analog 421, along with its probe sensor, operates as a capacitance sensitive system that converts changes in level to changes in the output signal. After calibration, any change in level is recognized and converted to an analog output signal (4-20mA or 0-10 Volts DC). The system will operate any standard 4-20mA DC or 0-10 Volts DC indicator. A digital display that can be calibrated in engineering units is available. This display is visible through the transparent cover of the remote amplifier.

The Cap Analog 421 system is available without relays or with one or two relays along with the standard analog outputs. The relay or relays can be calibrated independently of the analog circuit.

The Cap Analog 421 is supplied with two 15 turns, ZERO and SPAN adjust potentiometers. The span control is independent and non-interacting. In addition, a rotary switch is provided to extend the range of the SPAN potentiometer.


R.F. Capacitance Remote Transmitter w/LCD

  • Onboard 3.5 digit LCD Display
    Scalable in engineering units
  • Two-wire transmission between electronics and probe
    Between electronics and probe
  • Built-in “coating tolerance”
    Designed to eliminate false signals caused by process material build-up/coating
  • Remote electronics for easy access
  • Up to two non-interacting and independently adjustable relays
  • Analog dampening for agitated vessels
  • Green LED for fault indication
    - Sensing probe failure
    - Wiring error
  • Up to one-mile separation
    Between probe and electronics
  • Sensing probes lengths to 250 ft.
  • Inverted output option


  • Supply Voltage:
    115 Volts AC
    230 Volts AC
    90-135 Volts AC
    180-279 Volts AC
  • Power: Less than 6 volt-amperes 
  • Frequency, AC Power: 50-60 Hz
  • Output: 4-20mA DC 600 ohms maximum with 24 Volts DC power supply or 0-10 Volts DC 
  • Analog Response: A unique circuit that provides output dampening for turbulent levels
  • Output 420-2: 2 Relays, 1 Form C SPDT switch each, in addition to analog output
  • Relay Ratings: 
    5 amp @ 115 Volts AC Non-inductive
    3 amp @ 230 Volts AC Non-inductive
    3 amp @ 2 Volts DC Non-inductive
  • Fall-Safe Switch Selectable (1 set each relay):
    High-Level Fail-safe Position: Relay is de-energized when liquid is present
    Low-Level Fail-safe Position: Relay is de-energized when liquid is not present
  • Indicators Status Lights: Two, light-emitting diodes (LED), RED - Illuminated when liquid is greater than setpoint, YELLOW - Illuminated when relay is energized
  • Digital Display:
    0.50 Inch liquid crystal
    3-1/2 digit, units -499 to 1,999
  • Temperature Range  Electronic: -40°F to +160°F (-40°C to +71°C) 
  • Zero (Terminal):
    Min. 10 pfd
    Max. 250 pfd
    Min. 10 pfd
    Max. 1,200 pfd 
  • Stability: 0.5 pf/30°F (at maximum sensitivity) 
  • Span:
    Standard Pre-Amp: Overlapping
  • Process Mounting Requirements: 3/4 N.P.T. (standard)
  • Pre-Amplifier Cast Aluminium with Fuse Polyester Finish:
    Meets NEMA 4, 5, 7, 9, 12;
    NEC Class I - Groups C, D
    NEC Class II - Groups E, F, G
  • Remote Amplifier Glass-Reinforced Polyester Enclosure, Stainless Steel Trim: NEMA 4X


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