Need input for valve stem sensor

[OkiePC]

I have a customer with a valve that has limit switches and what I think is a rotary potentiometer for position feedback. The analog sensor gives a a very flaky reading (4-20mA input to a Micrologix 1400 via 1762-IF4).

Both of the limit switches are froze up. This is in a vault that is covered but exposed to moisture and temperature extremes.

I was thinking about using proximity sensors for the end limits but it might make more sense to use a laser distance sensor or something similar and just do away with the limit switches. If I can get a very repeatable analog sensor I think this could work well.

I think the object on the stem is made of stainless steel so a long range inductive prox could work for limit switches. I believe the travel range of the stem is around 4 inches, but I am not certain of that. The only laser distance sensor I ever worked with was something like ten meter range and in a relatively clean climate controlled setting.

Tell me what you think:

 

[g.mccormick]

How about a LVDT? You can even get them with 4-20MA outputs

http://www.omega.com/pptst/LD630.html

 

[OkiePC]

How about a LVDT? You can even get them with 4-20MA outputs

http://www.omega.com/pptst/LD630.html

Hadn't considered it due to price. Seems the prices have come down quite a bit. Good idea.

 

[g.mccormick]

I don't know your needed stroke, but here is a cheaper version with IP67 protection level.

http://www.omega.com/pptst/LDI-127.html

LDI-127-100-A020A $455.00 2 In Stock
Linear sensor, 100 mm range, 27 mm housing, radial cable, rodeye ends, 4 to 20 mA output

 

[Tom Jenkins]

Try contacting the valve operator manufacturer. They often have standard kits available for sensing, and should have them in NEMA 4X.

 

[John Morris]

short/small/ programmable for 4-20, IP67

http://www.directindustry.com/prod/leuze-electronic-gmbh-co-kg/product-4741-1823977.html

Can't tell the price. They want a log in, and then you get all the junk mail.......for years

 

[OkiePC]

Thanks for the input on this. The valve is made by Singer so I will reach out to them too. The ultrasonic may be worth checking into also.