DC Digital Panel Meter Frequently Asked Technical Questions
In Laureate DC meters, a total of five DC voltage ranges and four DC current ranges are user selectable and factory calibrated, with calibration factors stored in EEPROM on the signal conditioner board. DC meters come factory set for a specific range, like DCV1. To change to a different range, move jumpers on the signal conditioner board and select the new range in software, as explained in Section 11 of the Laureate DPM user manual. If you change the range, also change the model number on the meter label.
Laureate DC 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.
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 a meter that displays units of DC voltage or DC current. The term “process meter” is 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.
A count is a unit of resolution. All ranges of Laureate DC meters are bipolar and are divided into ±20,000 input counts. For example, in the Laureate ±200.00 mV DCV1 range, an input count is 0.01 mV. The Laureate ±600.0V DCV5 range and ±300.0V DCV6 range are both based on a fictitious ±2000.0V range, so an input count is 0.1V. The Laureate ±5.000A DCA4 range is based on a fictitious ±20.000A range, so an input count is 0.001A.
A display count, also called output count, is the resolution of the meter reading, or the step value of the least significant digits. For example, a meter reading of 465.7 is 4657 output counts. The decimal point is set separately as a decoration.
Input scaling is the process of converting the input counts to a reading in display (or output) counts. For example, to convert the 0-50.00 mV DC output of a current shunt to a 0-800A DC reading, use the DC meter’s ±200.00 mV DCV1 range. 50.00 mV is then 5000 input counts. 800A is 800 display counts. To go from 5000 to 800, enter a scale factor (or multiplier) of 0.1600 and an offset of 0.
Analog output scaling is the process of converting the meter reading to an analog output. That output can be selected as 4-20 mA, 0-20 mA, 0-10V or -10 to +10V. Simply enter the DC meter readings for the bottom and tops of the 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 that range in software and scale it in software, and connect to the designated analog output pins, as explained in Section 17 of the Laureate DPM user manual.
Calibration is the process of setting the meter so that absolute readings in volts or amps are within specified tolerances of a recognized national standard. All ranges of Laureate DC input and DC analog output boards are factory calibrated to standards of the US National Institute of Standards and Technology (NIST), with calibration factors stored in EEPROM on the board itself. This allows boards to be swapped in the field with not need to recalibrate the meter as a system.
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 outside calibration labs and by customers by 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 or DC current standard is required. Also required in the meter is a communications board, like the Laureate USB interface board P/N LUSB. Following calibration, that board can be removed and be used in another meter.
The Laureate DCA4 current range accepts DC currents up to ±5.000 amps. For higher currents, use an external current shunt with the meter’s sensitive ±200.00 mV DCV1 voltage range where each input count is 0.01 mV. A current shunt, available from multiple suppliers, is an accurate, very low resistance R resistor which is placed in line with the current I to generate a low voltage drop IR. Shunts are characterized by their maximum current, such as 500A, and the corresponding IR voltage drop, which is typically 50, 75 or 100 mV. Scale the meter to convert the measured input counts, which are units of 0.01 mV, to DC amps.
The highest DC voltage that be applied to a Laureate DC meter is ±600.0V when the meter is set to the DCV5 range. For higher voltages, use an external high voltage resistor or string of resistors in series with meter’s 10 Meg input resistance to create a voltage divider. For example, to measure 0-1000V DC, use an external 50 Meg, 1 Watt resistor in series with the 10 Meg input resistance of the DCV6 range to create a 6:1 voltage divider. The meter then senses a safe 0-166.66V DC with 0.01V resolution when set to the ETL certified 300.0V DCV6 range. Apply a scale factor of 6.0000 to display 0-1000.0V DC. Laurel has equipment to calibrate the meter and external resistor as a system up to 1020V.
Yes, the Laureate DC/process meter can be used as a load cell meter in four-wire bridge mode, but its sensitivity is limited to 10 microvolts per count. It can apply 5V or 10V excitation and work in a ratiometric mode. In that mode, the excitation voltage is also used as the reference for the analog-to-digital converter, thereby automatically correcting for variations in excitation voltage. The 5-digit meter display can be scaled to read out in engineering units, such as units of weight or pressure. However, the Laureate load cell meter is preferred for demanding load cell applications, since it offers a higher sensitivity of 1 microvolt per count. The load cell meter also allows a 6-wire connection while the DC/process meter only allows a 4-wire connection.
Yes, the Laureate DC/process meter is ideal for potentiometer sensor applications used for displacement or angle measurement. Such sensors work as a voltage divider, where a fixed voltage is applied to endpoints of a resistive element and a voltage is picked off as a sliding contact is moved along its length. For such applications, the Laureate DC/process meter applies an excitation voltage of 5V DC and uses its 20.000V DCV3 range. It works in a ratiometric mode where the excitation voltage is also used as the reference for the analog-to-digital converter, thereby automatically correcting for variations in excitation voltage. The picked-off DC voltage is scaled by the meter for readout in percent or in engineering units, such as millimeters, as programmed.
