Laureate DC meters and process meters are the same and are covered by the same Section 11 of the Laureate DPM user manual. The term “DC meter” is used for any meter that displays units of DC voltage or DC current. The term “process meter” is typically used for a DC meter that accepts an industry standard 4-20 mA or 0-10V DC signal and converts that signal to engineering units using scale and offset adjustment, also called zero and span adjustment. All Laureate DC meters are user scalable regardless of range. The ±20.000 mA DC range is used for the 4-20 mA process range.
Also called a “potentiometer follower meter,” a ratiometric metric displays the ratio of a signal voltage to an applied excitation voltage. The typical sending device is a potentiometer where a DC excitation voltage is applied across a resistive element and the signal to be measures is picked off by a contact that slides along the length of that element. Linear potentiometers are used to measure linear displacement in inches or mm. Rotary potentiometer are used to measure angular displacement in degrees or radians. For use as ratiometric meters, Laureate process meters need to be jumpered for 5 Vdc excitation and be programmed for ratiometric operation.
Laureate process meters whose model number ends with P or P1 and load cell meters whose model number end with WM1 can be used with the same types of load cells and can scale millivolt signals for display in engineering units. Limitations of the Laureate process meter compared to the load cell meter are that its resolution is limited to 10 microvolts, not 1 microvolt, and load cell connections are limited to 4 wires, not 6 wires. The slightly more expensive load cell meter is recommended for higher resolution readings.
Both signal types have been popular analog output standards for transducers and transmitters for decades. Both signals are electrically safe. 0-10V is commonly used in labs and test stations where cable runs are short and electrical noise is not a problem. 4-20 mA is used in industrial environments and for long cable runs since the current signal is active and is not affected by cable resistance or electrical noise pickup. Also, 4 mA serves as an active zero to indicate normal operation, while 0 mA would indicate a cable break or other electrical failure.
Yes they can. Laureate process meters can be jumpered for an electrically floating 24 Vdc up to 50 mA excitation output, which is electrically floating and can be used to power the transducer or transmitter that controls the 4-20 mA current signal. Please see the 2-wire wiring diagram on page 6 of the Laureate DPM user manual.
A count is a unit of resolution. For the Laureate DC and process meter, each input range is ±20,000 counts. The 0-10V process range is 0-10,000 counts using the ±20.000 Vdc range. The 4-20 mA process range is 4,000-20,000 counts using the ±20.000 mAdc range. Display counts, also called output counts, are the values to be displayed as readings. For example, a reading of 2465.7 lbs is 24657 output counts. The decimal point is set separately as a decoration.
Process meter scaling is the process of converting the meter’s input counts to a reading in engineering units, which are display or output counts. For example, if a Laureate process meter with a model number ending in P is set to the factory default input rang of 4.000-20.000 mA, scaling would allow this range to be displayed as 0-100.0 (PSI).
Under the front panel menu item “Setup,” select the “Coordinates of 2 points scaling method.” Enter Lo In, Lo Rd, and Hi In, Hi Rd. For the above example, enter 4.000 for Lo In, 0.0 for Lo Rd, and 20.000 for Hi In, 100.0 for Hi Rd.
If the process meter model number has a P suffix, this indicates that that it came with factory default scaling, which is a 4-20 mA input scaled to display 0.00 to 100.00 (%). If the process meter model meter has a P1 suffix, this means that it was ordered with custom factory scaling, which was specified as Lo In, Lo Rd, and Hi In, Hi Rd. Both the factory default P scaling and factory special P1 scaling can easily be changed by the user by selecting one of the meter’s 5 jumper selectable DC voltage ranges or 4 jumper selectable DC current ranges, and scaling the meter from the front panel, as explained in the Laureate DPM user manual.
Laureate process cell meters are modular with slots for an analog output board, a choice of relay boards, and a choice of communication boards, as illustrated in our Laureates Overview web page. These boards can be ordered installed with a new meter, but they can also be purchased separately later and be simply plugged in. The presence of a new board and the type of board are automatically sensed by the meter’s firmware or by Instrument Setup (IS) software. If you change boards, also change the model number on the meter label.
Input calibration is the process of setting the process meter in software so that absolute readings in are within specified tolerances of a recognized national standard. Electrical input calibration is required for operation of the process meter as a DC voltmeter or DC ammeter. It is also required when the meter is scaled using the scale and offset method or the coordinates of 2 points method, both of which require correct absolute DC voltage or DC current readings. Electrical input calibration is not required for the reading coordinates of 2 points scaling method, which uses actual weights or other know physical standards for calibration, not known electrical signals.
Annual calibration to NIST standards can be performed by Laurel and by some of its distributors as a service. It can also be performed by the customer using Laurel’s free Windows based Instrument Setup (IS) software. Open the Main Menu of IS software, click on Calibration in the top menu bar, and follow the prompts. An external DC voltage standard is required. Also required in the meter is a communications board, like the Laureate P/N LUSB USB interface board. Following calibration, that board can be removed and be used in another meter.
Analog output scaling is the process of converting the meter reading to an analog output, which can be user selected as 4-20 mA, 0-20 mA, 0-10V or -10 to +10V. Simply enter the process meter readings for the bottom and tops of the selected analog output range, and the output will be interpolated linearly between these two readings. Please see Section 17 of the Laureate DPM user manual.
Chances are that your meter is set for the factory default analog output, which is 4-20 mA, and is applying 10V to force a current into an open circuit. To set your meter to a 0-10V or -10 to +10V analog output, set jumpers for unipolar 0-10V or bipolar -10 to +10V operation, select the desired range and scaling, and connect to the correct analog output pins, as explained in Section 17 of the Laureate DPM user manual.