Only 1 channel works on 2

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JRD
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Only 1 channel works on 2

Postby JRD » Tue Mar 23, 2021 3:28 pm

I bought last week an EGT-K 2ch amplifier (order N°263949553)

Today I wanted to control the operation of the amplifier
The amplifier is fed in +12V by a stabilized power supply and 2 K-type sensor probes are connected to the inputs.

Channel #1 works well, but #2 does not:
- The Output 2 always stay at 0,100mv with a sensor probe connected to Input 2 and despite this probe being in boiling or cold water.
- With no sensor probe, Output goes up to 5V
- The inversion of the 2 probes does not change anything

How can I fix this problem?

ArT
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Re: Only 1 channel works on 2

Postby ArT » Wed Mar 24, 2021 8:15 am

It seems like channel is working but it's detecting short circuit on input (TC+ connected to TC- will give amplifier temperature -> 0,100V is about 25C). Disconnected TC+ and TC- will give +5V output (~1250C). When you disconnect sensor and you have +5V output it means that short circuit is not in amplifier but in external circuit (maybe probe is faulty and is doing short circuit?). When you connect TC+ to TC- and you have about 0,100mV it means that amplifier is working fine.

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Re: Only 1 channel works on 2

Postby JRD » Thu Mar 25, 2021 1:21 pm

Hi,

I did some more test to understand the problem, the amplifier is still supplied with 12V by a stabilized power supply.

- without any input or output connected element, I measure 5V on the output terminals
- after connecting the probes directly to the input terminals, I measure 94mv on output 1 and 99mv on output 2 (probes at room temperature, measure directly on the terminals)
- the inversion of the 2 probes gives me exactly the same result (94mv on output 1 and 99mv on output 2)
- when I dip the probes in boiling water, I measure up to 404mv on output 1 and always 99mv on output 2
- the inversion of the 2 probes gives me exactly the same result (up to 404mv on output 1 and 99mv on output 2)

My probes cannot be questioned since both work very well on channel 1 and give consistent values for boiling water (404mv = 101°C)

If there’s a short circuit, it’s in the amplifier.
But I couldn’t highlight it with the multimeter

ArT
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Re: Only 1 channel works on 2

Postby ArT » Thu Mar 25, 2021 2:14 pm

Could you check the resistance between TC+ and TC- for first channel and for second channel, please? (amplifier should be NOT powered, thermocouples should be disconnected)

JRD
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Re: Only 1 channel works on 2

Postby JRD » Fri Mar 26, 2021 7:42 am

19.49 MΩ between VCC and GND
7.17 M Ω between TC1+ and TC1-
1.014 M Ω between TC2+ and TC2-
9.66 kΩ between GND and Out1
9.66 kΩ between GND and Out2

Everything is disconnected

ArT
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Re: Only 1 channel works on 2

Postby ArT » Fri Mar 26, 2021 12:09 pm

JRD wrote:19.49 MΩ between VCC and GND
7.17 M Ω between TC1+ and TC1-
1.014 M Ω between TC2+ and TC2-
9.66 kΩ between GND and Out1
9.66 kΩ between GND and Out2

Everything is disconnected


You are right and something is wrong with 2nd channel, it's not short circuit but resistance should be higher. I'll send you replacement. Please check your PM I'd like to confirm your address for delivery.

JRD
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Re: Only 1 channel works on 2

Postby JRD » Fri Apr 02, 2021 12:37 pm

I received the new one yesterday.
It works very well.
Thank you for your responsiveness


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