FID not heating

[skunked_once]

GC: HP 5890 Series II

My FID is not heating. Actually, is is warm to the touch. The setting on the front panel is 300 C and the readout says 300 C but I can hold my fingers on it so it is not 300 C.

Any ideas?

[GasMan]

I would go for the sensor, but before you change that I would set the temperature to 400°C and see if the temperature increase to "400°C" indicated. If this happens you will know that the heater and control circuit are OK. If it does not change, then go for the sensor

Gasman

[uzman]

Was the detector temperature started from room temperature then went to 300 C ?
If this is the case , the sensor is o.k.

Did you wait enough time for equilibration before touching the detector ?
It needs some time for the temperature to reach the upper parts and the upper parts of the detector can never reach 300 C.

The temperature is controlled around the bottom part of the detector where flame jet is located.

[skunked_once]

Thanks for the suggestions. I have completely disassembled the detector and found out that the heater probe is heating. After careful reassembly, the detector readout reads 250 but I can still hold my fingers on the upper housing. The nut inside the column oven is too hot to touch. Now there is another problem. I cannot get the flame to stay lit. Air and hydrogen flows were checked with a bubble flowmeter and are correct (air = 300-330 mL/min and hydrogen = 30-40 mL/min). The ignitor glows and some weak pops result but the flame goes out as soon as the ignitor button is released. Aaaaarrgggg!!! Any ideas would be much appreciated.

[dblux_]

... I cannot get the flame to stay lit. Air and hydrogen flows were checked with a bubble flowmeter and are correct (air = 300-330 mL/min and hydrogen = 30-40 mL/min). The ignitor glows and some weak pops result but the flame goes out as soon as the ignitor button is released. Aaaaarrgggg!!! Any ideas would be much appreciated.

make up flow = ?

check lit offset

is it possible that FID heater consist of 2 sections, one for lower part and 2nd one for upper part of FID (and upper section is defective) ?
----------------------------------------------------
edit: impossible, there is only one heating cartridge

[cleh]

Heating problem could be electronic, but most of the time it's the sensor. If you can hold your fingers on it, it's not really 250. As far as the flame goes, leak check the detector and as dblux_ asked, what is your make up flow? Sometimes if you turn off the air and hold the ignitor button down while turning the air back on it may stay lit. Please let us know what you find.

[dblux_]

I agree with cleh.
It's not possible that column nut inside oven is 250 degC (provided oven is switched off) and upper housing is cool and can be touched. Temperature distribution across FID is much more uniform.

Problems with flame may be connected with defective temperature sensor as well. When sensor measures temperature below 150 degC FID logic cuts hydrogen and air flow and wait until temperature reaches >150 degC.

[Bigbear]

Not unusual. The heater is down near the jet. The chimney exposed to room temp is often cooler than what you set the detector for.

[Consumer Products Guy]

I cannot get the flame to stay lit. Air and hydrogen flows were checked with a bubble flowmeter and are correct (air = 300-330 mL/min and hydrogen = 30-40 mL/min). The ignitor glows and some weak pops result but the flame goes out as soon as the ignitor button is released. Aaaaarrgggg!!! Any ideas would be much appreciated.

Have you cleaned the FID jet with the correct-sized cleaning wire, then with methanol?

Is your make-up gas on or off while you are trying to ignite.

Have you blown directly but very gently into the FID chimney while trying to ignite?

[James_Ball]

I agree with cleh.
It's not possible that column nut inside oven is 250 degC (provided oven is switched off) and upper housing is cool and can be touched. Temperature distribution across FID is much more uniform.

Problems with flame may be connected with defective temperature sensor as well. When sensor measures temperature below 150 degC FID logic cuts hydrogen and air flow and wait until temperature reaches >150 degC.

Did the 5890 Series II have the temperature lockout or did that start with the 6890? Also would depend if it has EPC or manual gas controls.

A partially clogged jet can often cause ignition problems when it gives a turbulent flow. When unlit, have you tried using a thermocouple inserted down into the detector to measure the temperature in the heart of the detector instead of just feeling the castle part?

For this model when we had a bad sensor we usually had very erratic temperature readings not just a steady low reading.

For me every FID wanted to light in its own way. Some needed makeup gas, some only lit without it. I have also had some that would not light with the ignitor but needed a butane lighter to light.

Since it was lighting but now isn't, I would disassemble and check jet and make sure all the spacers and seals are there correctly, and make sure the column end is not jammed into tip of the jet causing problems.

[dblux_]

James, you are right.

HP 5890 II probably has no minimum temperature limit of FID ignition nor it has lit off monitor.

[AICMM]

skunked_once,

One, I have found the heat distribution in the HP FID to be very poor. The heater is way down there and the chimney is way up here. Having said that, you want to leave the thing hot all the time so that heat builds up in the upper part of the detector. This means you should leave column flow on all the time. Your other option is to add a chimney heater if you have a second detector heater available (or you can afford to buy one from someone like Restek.) I can discuss this more if you would like.

Two, don't try to light it without it being hot for at least an hour or two. There is no minimum in the 5890 but you should allow it to get toasty.

Three, I have found that using the on/off controllers will lead to problems after a while. Problems being inconsistent flow rates on the detector. I prefer to use an on/off valve and a separate pressure controller for the FID hydrogen. Then I leave the knobs on the front on all the time.

Four, finally!, I sometimes have to start lean and work to rich to get it to light. Easiest to do this with low H2 pressure, light it, and then bring up the H2 pressure to a point where you want to run.

Best regards,

AICMM

[cleh]

Agree with deblux_ and James. The 5890 does not have the temperature lockout .

Also agree with James. The sensor usually shorts out so you will see fluctuating temps or the 5890 will shut down all of the heated zones because it thinks the heater is at it's max temp. I had a few situations when the sensor has read back improper temps so I do think it could be a bad sensor.

One other thought. What is your initial oven temp? If you did any maintenance on the FID before this started, is all of the insulation in place around the FID? If your oven temp is set at a similar value as the detector and there isn't enough insulation between the FID and the oven, the sensor could be picking up the oven temp and think the detector is at the correct value. Please let us know what you find.

[Stunt]

I haven't worked on a 5890 in some time, but I replace the heater/sensor assembly in my 6890 FIDs all the time. The thermocouple is a cylinder that heats via electric current, and the sensor is a smaller ceramic cylinder. Both insert into the heater block, and the ceramic sensor is generally a piece of crap that breaks as it heats and cools. If you have a secondary FID I would CAREFULLY switch out the entire assembly. Don't break that little ceramic piece or youre out two FIDs. I believe the part isnt very expensive, ~ $250?

[dblux_]

... The thermocouple is a cylinder that heats via electric current, and the sensor is a smaller ceramic cylinder. Both insert into the heater block, and the ceramic sensor is generally a piece of crap that breaks as it heats and cools. If you have a secondary FID I would CAREFULLY switch out the entire assembly. Don't break that little ceramic piece or youre out two FIDs. I believe the part isnt very expensive, ~ $250?

In fact a thermocouple can't be used as heater but as temperature sensor.
And heating element consist of resistance material.

best regards