Fluke 5500A Multi-Product Calibrator Fluke Corporation 1

Measuring Relative Humiditywith the Fluke 5500A

Multi-Product CalibratorApplication Note

The need to measurerelative humidityand temperatureMost quality standards and cali-bration procedures require thatrelative humidity and tempera-ture be recorded at the time ofcalibration. For most establishedlaboratories, this requirement ismet using mechanical recorderscalled hygrothermographs.Though hygrothermographs areperfectly adequate in these ap-plications for new laboratoriesor for on-site work, they repre-sent another instrument thatneeds to be purchased, cali-brated and taken to the job site.

The 5500A Multi-Product Calibrator is rugged, portable and covers a wide range of electrical calibration workload,including measurements of temperature and relative humidity.

The Fluke 5500A is a uniqueclass of multi-product calibratordesigned to calibrate a verywide range of electrical andelectronic measurement tools.It is also rugged and portable,making it suitable for on-sitework. This application notedescribes how the 5500A canbe used to record temperatureand relative humidity at thetime of calibration.

The 5500A features an inter-nal, single range voltmeter con-nected to the front panel at thethermocouple terminals.

Normally, this circuitry is usedto calibrate thermocouple simu-lators or to measure the outputof a thermocouple. Using a ther-mocouple, measuring tempera-ture with a 5500A is straight-forward. Can the same thingbe said for relative humidity?

The 5500A’s “MEAS TC”mode measures ±330 mV dcwith 0.005% uncertainty. Thecold junction compensated inputtemperature is displayed on theleft-hand output display, andthe actual measured voltage onthe right-hand control display.

2 Fluke Corporation Fluke 5500A Multi-Product Calibrator

See Figure 1. Regardless ofthermocouple type selected,the right-hand control displayalways shows the true inputvoltage to the 5500A. The inter-nal cold junction compensationis electronic and has no affecton this measured value. Usingthe voltmeter capability of the5500A, you can measure rela-tive humidity using an accessorydesigned for digital multimeters.

5500A compatibletemperature andhumidity probeVaisala manufactures a line ofprobes called theMultiMeterMate.TM These self-contained relative humidity andtemperature-to-voltage convert-ers come in two models, theMMM RH for measuring relativehumidity only and the MMMRH/T for measuring both rela-tive humidity and temperature.Each outputs 1 mV per % rela-tive humidity (%RH) or 1 mV perdegree of Celsius or Fahrenheit.They are designed to be con-nected to any high impedancedigital multimeter (DMM) thataccepts shrouded banana plugs.

The 5500A “MEAS TC” terminalsare subminiature thermocoupleconnectors widely used in tem-perature applications. To workwith the 5500A the probe con-nectors need to be modified.

You will need to remove theshrouded banana plugs andattach a subminiature coppermale connector in their place.Cut the leads of theMultiMeterMate on the coiledend of the wire assembly tomake it easier to attach thesubminiature thermocoupleconnector. Strip away 3/4" of theoutside black insulation to ex-pose the red and white leads.The red lead is the positiveoutput and is connected to thethin blade of the subminiatureconnector. The white lead is thenegative output and is con-nected to the wide blade.Figure 2 shows a convertedprobe. The subminiature con-nectors are available from dis-tributors such as OMEGA Engi-neering (order catalog numberSMP-U-(M), the uncompensated(copper) male connector). Con-tact Vaisala for your nearestdistributor to purchase theMultiMeterMate. Phone numbersand addresses are listed at theend of this application note.

Operation from the5500A front panelTo use the 5500A with aMultiMeterMate probe from thefront panel, select “MEAS TC”mode and choose the “10 µV/°C”linear thermocouple type. Theoutput of the MultiMeterMate isdisplayed in right-hand windowunder “Meas@TC terminal”. Thisis the actual voltage generatedby the probe. The “REF SRC”can be either external or inter-nal. The right display does notinclude any cold junction com-pensation. Note that wheneither probe is in the “OFF”position, the internal 9V batterywill be connected to the TCterminals. This causes the5500A to trip into standby anddisplay an error message.Keep the probe in either thehumidity or temperature modewhen attached to the 5500A.With the MMM RH/T, going fromtemperature mode to humidity

Figure 1. The 5500A in “MEAS TC” mode. The left-hand output display shows the inputtemperature. The right-hand control display shows the actual uncompensated input voltage.

Figure 2. The Vaisala MultiMeterMate Humidityand Temperature Probe with the subminiaturethermocouple connector attached.

Fluke 5500A Multi-Product Calibrator Fluke Corporation 3

mode causes the switch to passthrough the “OFF” position, butdoes not cause the 5500A totrip. In general, the 5500A TCterminals are protected againstdamage for inputs up to ±12V.

Remote operationIf your 5500A has software revi-sion 1.5 or greater (as shownunder “SETUP, UTILITYFUNCTNS, INSTMT CONFIG,SHOW SOFTWARE VERSIONS,Main”), you can also read theright-hand display voltagedirectly over the remote inter-face. Set the thermocouple typeto TC_TYPE X (10 µV/°C), andactivate the measure thermo-couple mode with TC_MEAS.The command to read the actualinput voltage is VVAL? Thiscommand returns “0E+00V” forany overload conditions.

If you have an earlier versionof 5500A firmware, you can stillobtain this same informationover the remote interface, butyou will need to read the tem-perature as shown in the left-hand output display, and scaleit accordingly. In this case, youshould set the “REF SRC” to“externl” and REF temperatureto “0.00”. The remote commandto do this is TC_REF EXT, 0CEL. Set the 5500A to the lin-ear output mode by sending thecommand TC_TYPE X as before.To return the measured value,send the VAL? command. Thisreturns the “temperature” asshown in the left-hand outputdisplay. Multiply this number by1e-5, and change the units tomV. Now, 1 mV representseither 1% RH or 1 degree.

Figure 3. Probe dimensions. (Dimensions are in millimeters.)

35

28.4

7.0 O18

3

18

21.5

14.5

O24

Vaisala MultiMeterMateTM Humidity and Temperature Probe

4 Fluke Corporation Fluke 5500A Multi-Product Calibrator

Fluke CorporationPO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.PO Box 1186, 5602 BDEindhoven, The Netherlands

For more information call:In the U.S.A. (800) 443-5853 orFax (206) 356-5116In Europe (31 40) 2 678 200 orFax (31 40) 2 678 222In Canada (905) 890-7600 orFax (905) 890-6866From other countries (206) 356-5500Web access: http://www.fluke.com

©1996 Fluke Corporation. All rights reserved.Printed in U.S.A. MultiMeterMate is a trademarkof Vaisala. B0308UEN Rev A

Printed on recycled paper.

4

3

2

1

0

-1

-2

-3

-4

10 20 30 40 50 60 70 80 90 100

RH

RH Accuracy of RH Measurement

0.7

0.5

0.3

0.1

-0.1

-0.3

-0.5

-0.7

10 20 30 40 50

Typical Accuracy of Temperature Measurement

-10

dT

T °C

5500A Multi-ProductCalibrator specifications5500A TC terminalsMeasurement range:±329.9999 mV dcResolution: 100 nVInput impedance: >100 MΩUncertainty:90 days: ± (0.005% of input +3 µV)1 year: ± (0.006% of input +3 µV)Protection: No damage forvoltages up to ±12V peakCommon mode voltage:20V peak maximum

MultiMeterMateTM Humidityand Temperature ProbespecificationsRelative humidityOperating range: 0 ... 100%Measuring range (for whichaccuracy is specified):0 ... 95% RHAccuracy (including nonlinearityand repeatability) whencalibrated against salt solutions(ASTM E104-85): See Figure 4Drift: Less than +1% RH per yearResponse time: 15sTemperatureOperating range: -19 ... +60°C(-2 ... +140°F)Measuring range (for whichaccuracy is specified):-10 ... +50°C (14 ... 122°F)Accuracy: See Figure 5OutputsRH-output (1 mV/%RH):0 ... 100 mV, equivalent to0 ... 100% RHT-output (1 mV/deg) selectable:When F selected:-2 ... 140 mV (°F)When C selected:-19 ... 60 mV (°C)Minimum meter inputimpedance @ 100 mV scale:10 MΩGeneralMeasuring element: 15778HM(RH), 1844 (T)Battery: Standard 9V batterySize: 6F22, 006P or NEDA1604Current consumption: 2 mAOperating temperature rangefor electronics: -19 ... +60°CStorage temperature:-40 ... +80°CEMC levels:IEC 801-2 Level 4IEC 801-3 Level 2IEC 801-4 Level 4EN55022 Class BHousing material: Plastics (ABS)Housing classification: IP40Probe cable (banana plugs): PVC

References• Fluke 5500A Operator

Manual, Chapter 6, RemoteCommands.

• OMEGA Engineering,The Temperature Handbook,TM

Vol. 28, page G-8.Telephone 1-800-826-6342(US and Canada).

• Vaisala, MultiMeterMateOperating Instructions,pages 1-2.

• Vaisala, MultiMeterMatedata sheetVaisala100 Commerce WayWoburn, MA 01801Telephone 617-933-4500

Figure 5. Typical accuracy of temperature measurement.

Figure 4. Accuracy of RH measurement.