Multifunction Process Calibrator

[Yashu]

I'm searching for a calibrator.

I'm eyeing up either the Martel MC-1200 -or- Fluke 726

I like the MC-1200's keyboard, but, we all know the Fluke name.

Does anyone have any comments on these units, or any other units, or any links to web pages offering reviews on calibrators.

 

[danw2]

I have heard gripes from techs who have the Flukes and who use Hart, about the inability of the Fluke to take updated HART DDs, the configuration files that are instrument model specific. It works OK with what it comes with, but if DDs for newly released devices are needed, there is some problem in getting them into the Fluke.

Whether this has been addressed by Fluke, I don't know.

The same techs love the Fluke for its conventional V & mA calibration modes.

I have found that some resistance input process instruments & recorders will not calibrate with anything but a pure resistance (decade box). Whatever means the electronic calibrators use to simulate a resistnace drives some model devices nuts. If you have RTD inputs on devices, you might want to check how the device responds to electronic simulation of resistance before commiting, or just know you're back in the world of decade boxes.

 

[Yashu]

Thanks danw,

Do you know what the CJC on/off setting does?

I don't understand why the TC accuracies get worse (according to the users manual) if CJC is enabled?

Do you know if CJC is implemented automatically within the cheaper Fluke 725? (i.e. can I operate the 725 in outside temps of say 40degF with good accuracy)

Thanks.

 

[itsmoked]

Isn't CJC = Compensation Junction?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

The CJC reading is added to the temperature determined by the mV reading. Any CJC error contributes directly to reading error. The error is not a percentage, it is a direct 'adder' (O.2).

There are those who can't tolerate that diminished degree of accuracy and resort to external cold junction compensation.

Some very critical calibration applications use a TC immersed in an icebath to ensure cold junction accuracy, which is verified with a certified liquid-in-glass thermometer.

Historically, there were applications where CJC was accomplished by measuring a reference temperature point assumed to be at a stable temperature and then biasing the calculation with the difference between the reference
temperature and the freezing point of water.

I think most of those have gone away, but should that be required, the CJC could be turned off and the reference temperature substituted.

I suspect that there is also a mode to output temp value in mV per the tables, which is what the old mV calibrators did, using copper wire connections.

In the 726 manual, it isn't clear what units the CJC error is in. Deg C?

The 725 manual states:
A thermocouple (TC) input/output terminal and
internal isothermal block with automatic referencejunction
temperature compensation. (page 11 pdf)

Dan