Omega DP3001 manual Signal Inputs

4.4SIGNAL INPUTS

RATIO: The reference input allows an external voltage to be used as the reference source for conversion. In this mode, the meter reads the ratio of the signal voltage to the reference voltage rather than the true value of the input.

Reading in Counts =	Signal Voltage	x 10000
	Reference Voltage

On the 20 V and 200 V ranges, the signal voltage must be scaled by 1/10 and 1/100, respectively. For all ranges, the standard reference input impedance ratio is 80 ohm. For 100 Mohm, open solder switch F on the main board (Figure 5.3). The reference voltage must be between the limits specified, +0.5 to +2.0 V, and must be positive with respect to analog ground.

HOLD: When high (or open), the A/D will free-run with equally spaced measurement cycles every 40,002 clock pulses. If taken low, the converter will complete the full measurement cycle and then hold this reading as long as HOLD is low. A positive pulse (greater than 300 ns) will now initiate a new measurement cycle, beginning with between 9,001 and 10,001 counts of auto-zero time. If the pulse terminates before the full measurement cycle (40,002 counts) is complete, it will not be recognized and the converter will simply complete the present measurement. An external indication that a full measurement cycle has been completed is that the first strobe pulse will occur 101 counts after the end of this cycle. Thus, if HOLD has been low for at least 101 counts, the converter is holding and ready to start a new measurement when pulsed high.

BLANKING: The display may be blanked by grounding the BLANKING input. The blanking input must be open for normal display operation. The polarity sign and decimal points are not blanked, but they will flash if the displayed reading exceeds ±19999 counts.

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