Contents

• Intro
• Exterior
• Analysis
• Performance test
• Tweaks and calibration
• Conclusion

Intro

Friend of mine wanted to have ability to calibrate his portable 3½-digit and 4½-digit DMMs, without spending too much money. So reference units, such as voltagestandard.com Pentaref are out of question, due to their cost. Also using ovenized reference circuits, such as LM399 or LTZ1000 would be major overkill for testing portable 4½-digit DMM anyway.

Choice was made for quad-output Analog Devices AD584K-based module from aliexpress.com (Taobao). But my friend did not trust values writted down on reference, so he asked my help to check references output and calibrate it if required. My Keithley’s Model 2001 capability should be fit well enough to perform this task, so I took the challenge.

Specification

According to deciphering label sticker on package, our unit was calibrated using 8½-digit DMM HP 3458A, somewhen in 2015, with ambient temperature +26°C with next data:

Voltage output mode	Labeled reading	Ambient temperature	Value off
2.500 VDC	2.50101 VDC	+26 °C	+404 ppm
5.000 VDC	5.00158 VDC	+26 °C	+316 ppm
7.500 VDC	7.50408 VDC	+26 °C	+544 ppm
10.00 VDC	10.00404 VDC	+26 °C	+404 ppm

• Module input voltage : from +14 to +30 VDC
• Input current : 10 mADC
• Output current, max : 5 mADC sink or source

Calibration temperature setpoint at +26 °C is unusual for test gear, as most of instrumentation is calibrated for +23°C.

Exterior

It was shipped in usual letter package, with good enough packing and multiple wraps of foam.

Nothing fancy at all, not even kelvin-sense for VREF output. Manufacturer even cheaped out with output film capacitor, as PCB footprint remained unpopulated.

Dual-layer PCB have very simple construction

Analysis

Before we go deep into testing, let’s take a good look on used voltage reference chip datasheet, AD584KH

Analog Devices AD584 datasheet, Rev.C

Analog Devices AD584 datasheet, Rev.B

Here’s most important specs from datasheet:

OUTPUT VOLTAGE TOLERANCE, Maximum Error for Nominal	Value	Unit
10.000 V	±10	mV
7.500 V	±8	mV
5.000 V	±6	mV
2.500 V	±2.5	mV
OUTPUT VOLTAGE CHANGE, Maximum Deviation from 25°C	Value	Unit
5V and above outputs	±5	ppm/K
2.5V output	±10	ppm/K
NOISE (0.1 Hz to 10 Hz)	Value	Unit
Typical	50	µV peak-peak
SHORT-CIRCUIT CURRENT	Value	Unit
	30	mADC
Absolute maximum input Voltage VIN to Ground	Value	Unit
	40	VDC

Performance test

K2001:

Declared on the bag : 7.50408 V , actual measured 7.504066 V
Declared on the bag : 2.50101 VDC , actual measured 2.501040
Declared on the bag : 5.00158 VDC , actual measured 5.001555
Declared on the bag : 10.00404 VDC, actual measured 10.004057

To do test I’ll use next equipment:

Test item	Instrument	Related spec	Calibration date
Power supply A	Keithley 2400 SMU	20VDC 20mA	2015
Power supply B	Pair of NiMH 9V cells	18VDC	N/A
Output voltage accuracy	Keithley 2001 DMM	20VDC range	Feb 2014
Output voltage accuracy	Keithley 2002 DMM	20VDC range	2007
Output voltage accuracy	Keithley 182-M voltmeter	3 and 30V ranges	2015
Output voltage noise	Keithley 182-M voltmeter	3mV range	N/A
Relative stability	EDC MV106 DC Standard	30ppm tempco	Feb 2014

Tweaks and calibration

Would be great to shield reference module more from careless use, as well as trim output voltages to be more accurate.

Conclusion

This reference is fine to test 4½-digit DMM points but nothing more than this.