Process & Ratio Meter

Digital panel meter / controller with scalable readout & control outputs for process signals such as 4-20 mA. Used to display pressure, level, flow, and more.

Process Meter


  • Reads process signals from ±200 mV to ±600V or ±2 mA to ±5A full scale
  • Ratiometric mode for bridges and potentiometers
  • Zero adjust from -99,999 to +99,999, span adjust from 0 to ±99,999
  • Error less than 0.01% of full scale for absolute ranges, less than 0.01% of reading for ratiometric measurements
  • Up to 60 readings per second
  • Transducer excitation output, 5, 10 or 24 Vdc (isolated)
  • Universal 85-264 Vac / 90 -300 Vdc or 10-48 Vdc / 12-32 Vac power
  • Wide choice of options:
    - 2 or 4 relays, mechanical or solid state (isolated)
    - Analog output, 4-20 mA, 0-10V, or -10V to +10V (isolated)
    - Serial data I/O: Ethernet, USB, RS485, RS232 (isolated)
    - Custom curve linearization, rate from consecutive readings

digital process meters are a cost-effective solution for process signals such as 4-20 mA, 0-10V, or 0-5V which require zero and span adjustment for monitoring and control applications. Full-scale voltage input ranges from ±200 mV to ±600V and current ranges from ±2 mA to ±5 A are jumper selectable. All ranges are precalibrated at the factory, so that recalibration is not needed when changing ranges or signal conditioners. The 200.00 mV and 2.000 V ranges provide a high input impedance of 1 Gohm to minimize the load on the voltage signal.

The meter can be set to a ratio mode (or potentiometer follower mode) by making a software selectiion. In this mode, the meter tracks a ratio of the applied excitation voltage and is unaffected by changes in the excitation voltage. This capability is used for resistive bridge sensors and voltage dividers, such as potentiometers which track wiper position. Ratiometric measurements provide an exceptional accuracy of 0.01% of reading ± 2 counts.

Scaling is from -99,999 to +99,999 (five full digits) with any decimal point to display readings in engineering units, such as PSI. Three scaling methods are user selectable: scale and offset, two-point method, and system-level calibration using actual transducer signals.

An isolated 5, 10 or 24 Vdc isolated excitation output is standard to power transducers or two-wire transmitters. Ratiometric operation, which automatically compensates for changes in the applied excitation, is jumper selectable for applications, such as bridges, where the signal to be measured is proportional to the excitation level.

High read rates at up to 60 or 50 conversions per second while integrating the signal over a full power cycle are provided by Concurrent Slope (US Pat 5,262,780) analog-to-digital conversion. High read rates are ideal for peak or valley capture, real-time computer interface, and control.

Peak and valley values are automatically captured. These may be displayed via a front panel pushbutton command or control signal at the rear connector, or be transmitted as serial data.

Digital filtering is selectable for electrically noisy environments, including a batch averaging filter and an adaptive moving average filter which provides a choice of 8 time constants from 80 ms to 9.6 s. When a significant change in signal level occurs, that filter adapts by briefly switching to the shortest time to follow the change, then reverts back to the selected time constant. In a selectable Auto filter mode, the filter time constant is automatically selected based on detected signal noise.

Auto-tare allows the display to be zeroed for any input signal by applying a switch closure or logic signal at the rear connector. The tare value is stored in non-volatile memory and is retained when power is removed.

An Extended computer board can display rate based on successive readings. It also allows exceptionally accurate custom curve linearization, for example to read out liquid volume or rate of flow in a horizontal cylindrical tank based on level reported by a 4-20 mA transmitter. For setup, up to 180 data points can be input into a computer spreadsheet or text file by the user. The computer then calculates spline-fit segments, which are downloaded into the meter.

Designed for system use. Optional plug-in boards for communications and control include Ethernet and other serial communication boards, dual or quad relay boards, and an isolated analog output board. s may be powered from 85-264 Vac or optionally from 12-32 Vac or 10-48 Vdc. The display is available with red or green LEDs. The 1/8 DIN case meets NEMA 4X (IP65) specifications from the front when panel mounted. Any setup functions and front panel keys can be locked out for simplified usage and security. All power and signal connections are via UL / VDE / CSA rated screw clamp plugs.

DC Voltage Range Resolution Input Resistance Error at 25°C
±200.00 10 µV 1 GΩ 0.01% of FS ± 2 cts
±2.0000 100 µV 1 GΩ 0.01% of FS ± 2 cts
±20.000 1 mV 10 MΩ 0.01% of FS ± 2 cts
±200.00 10 mV 10 MΩ 0.01% of FS ± 2 cts
±300.00 0.1 V 10 MΩ 0.01% of FS ± 2 cts
±600.00* 0.1 V 10 MΩ ± 0.4 V
* ±600.00V range not ETL certified

DC Current

DC Current Range Resolution Input Resistance Error at 25°C
±2.0000 mA 0.1 µA 100 Ω 0.01% FS ± 2 cts
±20.000 mA 1.0 µA 10 Ω 0.01% FS ± 2 cts
±200.00 mA 10 µA 1 Ω 0.01% FS ± 2 cts
±5.000 A 1 mA 0.01Ω ± 10 mA

DC Voltage & Current

Readout 5 LED digits, 7-segment, 14.2 mm (.56"), red or green.
Range -99999 to 99999 or -99990 to 99990 (count by 10)
Indicators Minus sign, 2 red LED lamps
A-to-D Conversion
Technique Concurrent Slope (Pat 5,262,780)
A-to-D rate 60/s at 60 Hz, 50/s at 50 Hz
Output update rate 56/s at 60 Hz, 47/s at 50 Hz
Display update rate 3.5/s at 60 Hz, 3/s at 50 Hz
Reading Accuracy
Error at 25°C 0.01% of full scale ± 2 counts (except 5A range) for absolute measurements.
0.01% of reading ± 2 counts for ratiometric measurements.
Span tempco 0.003% of reading/°C
Zero tempco 0.1 count/°C
Noise Rejection
CMR, DC to 60 Hz 130 dB
NMR at 50/60 Hz 90 dB with min filtering
Maximum Signal
Max applied voltage 600 Vac for 20, 200 and 300 V ranges, 125 Vac for other ranges
Current protection 25x for 2 mA, 8x for 20 mA, 2.5x for 200 mA, 1x for 5 A
Voltage, standard 85-264 Vac or 90-300 Vdc
Voltage, optional 12-32 Vac or 10-48 Vdc
Frequency DC or 47-63 Hz
Power  consumption (typical, base meter) 1.2W @ 120 Vac, 1.5W @ 240 Vac, 1.3W @ 10 Vdc, 1.4W @ 20 Vdc, 1.55W @ 30 Vdc, 1.8W @ 40 Vdc, 2.15W @ 48 Vdc
Power Isolation 250V rms working, 2.3 kV rms per 1 min test
Excitation Output (standard)
5 Vdc 5 Vdc ± 5%, 100 mA
10 Vdc 10 Vdc ± 5%, 120 mA
24 Vdc 24 Vdc ± 5%, 50 mA
Output Isolation 50 Vdc to meter ground
Ratiometric operation Selectable at connector and in software
Analog Output (optional)
Output levels 4-20 mA, 0-20 mA, 0-10V, -10 to +10V (jumper selectable)
Current compliance 2 mA at 10V ( > 5 kΩ load)
Voltage compliance 12V at 20 mA (< 60Ω load)
Scaling Zero and full scale adjustable from -99999 to +99999
Resolution 16 bits (0.0015% of full scale)
Isolation 250V rms working, 2.3 kV rms per 1 min test
Relay Outputs (optional)
Relay types 2 Form C contact relays or 4 Form A contact relays (NO) 2 or 4 Form A, AC/DC solid state relays (NO)
Current tatings 8A at 250 Vac or 24 Vdc for contact relays 120 mA at 140 Vac or 180 Vdc for solid state relays
Output common Isolated commons for dual relays or each pair of quad relays
Isolation 250V rms working, 2.3 kV rms per 1 min tes
Serial Data I/O (optional)
Board selections Ethernet, Ethernet-to-RS485 server, USB, USB-to-RS485 server, RS485 (dual RJ11), RS485 (dual RJ45), RS232.
Protocols Modbus RTU, Modbus ASCII, TDM ASCII protocol
Data rates 300 to 19200 baud
Digital addresses 247 (Modbus), 31 (TDM ASCII),
Isolation 250V rms working, 2.3 kV rms per 1 min test
Signal Connections
Operating temperature 0°C to 55°C
Storage temperature. -40°C to 85°C
Relative humidity 95% at 40°C, non-condensing
Protection NEMA-4X (IP-65) when panel mounted

Ratiometric (or potentiometer follower) applications

In the application shown, the signal from a sliding contact voltage divider can be converted to engineering units such as position, level or percentage. By operating in a ratiometric mode, the meter automatically remove any effects caused by variations in the excitation supply. For use with a 1 kohm potentiometric source, the recommended applied excitation voltage is 10V. A 2 kohm resistor should be placed in series with the excitation output and excitation return leads. This allows the meter's 2.0000 V scale with a high input impedance of 1 Gohm to be used.

Powering two-wire transmitters

The isolated 24 Vdc, 50 mA excitation output, which is standard with all meters, is ideal for powering two-wire, 4-20 mA transmitters. The same two wires are used to apply voltage and carry the output current. Inside the meter, the 4-20 mA current is dropped across a 10 ohm resistor and sets up a 40-200 mV voltage, which is then sensed by the meter and scaled to engineering units.

Testing with peak detection

Destructive testing is an ideal application for the strain meter. Peak readings are automatically captured at rates up to 60 per second, while the display updates at a legible 3.5 readings per second. The peak reading can be recalled at the push of a button or be transmitted via RS-232 or RS-485. The meter provides isolated 10 Vdc power for up to four (4) the strain gauges and can be scaled to read out directly in engineering units from -99,999 to +99,999.

Custom curve linearization

The DC meter with the Extended main board option allows exceptionally accurate custom curve linearization. For setup, up to 180 data points can be entered into a spreadsheet. The system then creates multiple non-linear spline-fit segments, which provide much better accuracy than linear segments. Illustrated, is the readout of volume of irregularly shaped tanks based on measured liquid level or pressure. Altimeters and thermistors are further applications

Rate from successive readings

The Extended computer board allows the display of rate based on successive readings, for instance flow rate based on changes in liquid level or static pressure in a tank. In the above illustration, the meter displays the rate in gallons at which a horizontal tank is being emptied. The input to the meter can be nonlinear, since only the linearized readings are compared for the determination of rate.

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