A Micro Series meter with the Standard counter main board and a voltage-to-frequency (V-to-F) signal conditioner board (shown to right) is able to accurately extract the square root of analog signals. The display is a full six digits. The three standard input ranges are 0-1 mA, 4-20 mA and 0-10 V. Special input ranges are available from the factory.
One application of the Standard V-to-F meter is to accurately display flow rate in engineering units, such as gallons per minute, from the 4-20 mA signal of a flow transducer with a linear or squared output.
Extended Counter Version
Batch Control with Linearized Total
The Micro V-to-F meter with the Extended counter main board can also totalize the linearized flow rate derived from the analog rate signal, count up to a preset value, or down to zero from a preset value for batch control. The analog input may or may not require linearization. In addition to rate and total, the grand total of the batches or the number of batches can also be displayed by pressing a front panel key.
Use of the Extended V-to-F meter as an up or down-counting batch controller requires the dual-relay output board option. One of the relays is dedicated to ON/OFF batch control. The other relay is available to slow down rate near the setpoint or to provide another alarm or control function based on rate or total.
One application of display of rate plus total is to read out kilowatts and kilowatt-hours based on 0-1 mA from a watt transducer.
Custom Curve Linearization
The relationship between the analog input and the value to be displayed can have a linear, square root, or custom curve relationship. For custom curve linearization, up to 240 data points can be input into a spreadsheet or text file by the user. The computer then calculates spline-fit segments, which are downloaded into the meter via RS232. Custom-linearized rates can be totalized and be used for batch control.
Like the Extended analog DC panel meter, the Extended V-to-F meter can linearize and display analog inputs based on a custom curve unrelated to flow, for instance to read out the volume of an irregularly shaped tank based on level or pressure, or to linearize a nonlinear transducer.
Time Based on Rate
The Extended V-to-F meter can display a time inversely proportional to measured rate, such as the time that it will take a conveyor to traverse an oven. As the rate of the conveyor is increased, the displayed baking time will be decreased.
Principles of V-to-F Operation
The V-to-F signal conditioner board converts the full-scale 0-1 mA, 4-20 mA or 0-10 V analog signal to a frequency of 10-110 kHz. This frequency is determined by measuring period over a selected gate time (from 10 ms to 200 s) and taking the inverse of period. Selecting a short gate time provides a much higher update rate than conventional counting-type frequency meters. At the lowest frequency of 10 kHz and the minimum gate time of 10 ms, the meter is capable of 25 updates per second.
Scaling to rate in engineering units and totalizing are done mathematically. Totals are stored in nonvolatile memory in case of power loss.
Micro Series meters can be powered from 95-240 Vac ±10% and 95-370 Vdc, or optionally from 12-34 Vac and 10-48 Vdc. Any setup functions and front panel keys may be locked out for simplified usage and security. The popular 1/8 DIN version with 0.56″ high digits is environmentally sealed to NEMA-4X (IP65) from the front when panel mounted, and is available with red or green LEDs.
High Resolution Display
The display of rate or total may be scaled to ±999,999. The two least-significant digits may be set to display zero with rounding or be active digits. In addition to a selectable gate time for rate measurement, an adaptive filter can reduce variations due to noise while rapidly responding to actual changes in signal level.
6 digits, 7-segment
Available with 0.56" or 5.0" digits.
High brightness red. Green available with 0.56" digits.
-99999 to +99999
Four LED lamps
Standard signal levels
0-1 mA, 4-20 mA, 0-10 V
Other signal levels
Gate time + 30 ms (max)
Selectable 10 ms to 199.99 s
Output & Display Updates
Same as conversion time
95-240 Vac ±10% and 95-370 Vdc
12-34 Vac and 10-48 Vdc
DC or 49-440 Hz
Safety-rated to 250 Vac, meter ground to earth ground,
DC to 60 Hz, 4.2 kVp per High Voltage Test
130 dB, DC to 60 Hz
5 Vdc ±5%, 100 mA max
10 Vdc ±5%, 120 mA max
24 Vdc ±5%, 50 mA max
50 Vdc to meter ground
0°C to 60°C
-40°C to 85°C
95% at 40°C, non-condensing
NEMA-4X (IP-65) when panel mounted
Flow from a Differential Pressure Transducer
An ideal application for the Standard Micro V-to-F meter: readout of flow based on the 4-20 mA analog signal from a differential pressure transducer. Options include dual relays for alarm or control, isolated analog output to turn the meter into a transmitter, and RS232 or RS485 serial communications.
Up- or Down-Counting Batch Controller
An ideal application for the Extended Micro V-to-F meter: up- or down-counting batch controller. The dual-relay card is required. One relay is dedicated to batch control, the other relay is available to alarm the rate or total. The signal input can be linear or nonlinear. The display can be toggled between rate and total.
Volume of an Irregularly-Shaped Tank
The Extended Micro V-to-F meter can linearize analog signals for display and alarm using custom curve linearization with multiple nonlinear segments. As illustrated, tank level is measured by an ultrasound detector, which transmits a 4-20 mA signal. This signal is then converted to a highly accurate volume reading. The linearized rate readings can also be totalized.
Process Time from an Analog Rate Signal
A unique application of the Extended Micro V-to-F meter: displaying process time based on the 4-20 mA or 0-10 V signal from a rate meter. In the above example, a tachometer transmits the speed of a conveyer belt through an oven. The meter displays baking time in the oven using the mathematical relationship time = distance / speed.