Actions
Forum Thread Details
  • Replies 19 replies
  • Subscribers 354 subscribers
  • Views 3897 views
  • Users 0 members are here
Related

Keithley DMM6500 Scanner Card - mystery component hidden in one of the channels

Jan Cumps

When I was wiring my Keithley 2000-SCAN card, I found a little component hidden inside the connector for channel 3. I hadn't spotted it before, just saw it during my work.
I initially thought it was a wire bridge used to measure the relay resistance. But it was a tiny component:

image

A little device on a ceramic chip.

I regret that I didn't take a photo first. Fortunately, I saw that it was visible on a photo I took for my first blog (and I hadn't deleted the original high resolution version yet):

image

I measured it, and it was around 100Ω. 108Ω actually. I thought that it could be a shunt for current measurement. But that's not very precise for a 100Ω resistor. When I touched it, I saw that the resistance increased fast. And that's when I realised it's a local temperature reference: Pt100 /RTD. The Pt100 is a common player in the measurement- and control (control theory) practice.

I found one on the e14 shop that looks very similar to the one embedded in my card: NB-PTCO-152  RTD SENSOR, THIN FILM PLATINUM, 100R. The photo on the Farnell page isn't the same, but the picture in TE's datasheet is very similar. The blackish look of the leads on my component seem to point that they are the silver version.

image

Mystery solved

link to all posts

Parents

  • Yesterday, I tried to put the device back inside the connectors. In channel 1, so that the default scripts for the DMM6500 would work.
    Unfortunately, even while I was careful, one of the leads of the Pt100 broke off. It was not a surprise - I was extra careful because I could feel that this was a weak point.

    Once I have saved some more equipment budget, I'll buy a new Pt100. Or if you have one that you can miss, send it to me.
    I'll post a comparison of temperature measurement, one with a simulated cold junction temp value, one with a Pt100 ...

  • in reply to Jan Cumps

    It's ridiculously easy to break the leads off them : ( I destroyed my only PT1000 that way too, barely flexed but its a weak point there. Does DMM6500 allow for thermistor params to be configured for cold junction compensation? Not as ideal but I've got at least a hundred of them here (mostly surface mount but easy to tack wires onto). I can easy shove a load of them into a envelope tomorrow.

  • in reply to shabaz

    I ordered a little set of 5 "RTD PT100 Tiny thin film type Class A".

    That 'll be enough to at least try to get one of them inside the screw terminals of channel 1 and let it sit there forever.

    I'm going to put that on channel one, because that's the assumption on the DMM6500 / 2000-SCAN combo when using a cold junction reference.

  • in reply to shabaz
    shabaz said:
    Does DMM6500 allow for thermistor params to be configured for cold junction compensation?

    Yes. And one of those options is to enter that temperature by hand. The error you make (if you just guess it) will influene the measurement error.

Reply Children
No Data